These are all known patch notes related to Warlocks, from newest down to oldest.

Patch 1.8.0 (11 October 2005)

• Death Coil - Cooldown reduced, mana cost increased, and now causes a short Fear effect that is not diminished.
• Corruption - Duration reduced and damage per tick increased. Total damage over duration approximately identical.
• Curse of Agony - Duration reduced to 24 seconds and damage per tick increased. Total damage over duration approximately identical.
• Conflagrate - Conflagrate will now correctly remove Immolate rank 4 from its victim when cast.
• Bane - Now reduces casting time of the Soul Fire spell in addition to Immolate and Shadow Bolt.
• Intensity - Now reduces chance to be interrupted during cast time of Rain of Fire, Hellfire and Soul Fire spells.
• Pyroclasm - Now gives a chance to stun when Rain of Fire, Hellfire, and Soul Fire spells damage the target.
• Soul Link - Percentage of damage split with pet has been reduced.
• Soul Link - Is now a spell cast on your pet that gives an aura to both you and the pet. This aura increases all damage caused by you and your pet by 3% and splits 30% of all damage taken by the caster to the pet. The aura will last as long as the pet is active, and the pet must be the target of a dispel effect in order to dispel this ability.
• Summon Felhunter - Has a new, unique sound effect.
• Lesser Invisibility (Succubus) - Tooltip updated to reflect actual functionality.
• Fixed a bug that would cause the Master Demonologist buff to be removed if the pet was banished.

Patch 1.7.0 (13 September 2005)

• Inferno - The stun effect can now be resisted. Tooltip updated to reflect enslave duration after the initial summon.
• Spell Lock (Felhunter) - In addition to interrupting spellcasting, it will now silence the target for a short duration.
• Benefits received from the old Master Conjuror talent should now be removed on all Warlocks.
• Firestone - When a Firestone is equipped, it should no longer interrupt tradeskill creation.
• Demonic Sacrifice - All effects gained from sacrificing the pet should no longer be dispellable.
• Conflagrate - The Conflagrate spell is now instant cast. The damage and mana cost has been raised on all ranks of the spell.
• Fear will now cause creatures to flee immediately, even if they are already moving.
• Succubus pets will be smarter about when to use Seduction.
• Succubus pets can now autocast Lesser Invisibility.
• Fixed a bug where Fear and Curse of Recklessness, when used together, would prevent targets from casting spells.
• Fixed a bug where Soul Link and Power Word: Shield, when used together, would heal the Warlock instead of splitting or absorbing damage.
• Demon Armor - The armor increase will now stack together with Scrolls of Protection.

Patch 1.6.0 (12 July 2005)

• Due to significant talent changes, Warlocks will have all talent points refunded and can be respent.
• Cripple (Doomguard) - Targets that are immune to movement slowing effects will no longer be affected by Cripple's movement slowing effect. Melee and ranged attack speed slowing effects will still affect these targets.
• Demon Skin/Demon Armor - Now increases health regeneration at all times, as was always intended. Previously, the health regeneration only occurred out of combat. Tooltips updated.
• Demonic Sacrifice - The sacrifice effects for the Voidwalker and Felhunter have changed. The Voidwalker will now regenerate 3% of your total health every 4 seconds. The Felhunter will now regenerate 2% of your total mana every 4 seconds.
• Demonic Sacrifice now works properly on banished summons.
• Summon Dreadsteed - New icon.
• Dark Pact - Fixed a bug where the combat log was reporting an incorrect value of mana gained by the caster when there wasn't enough mana to drain from the pet.
• Phase Shift (Imp) - While phase shifted, the imp is now targetable but will remain an invalid target for all spells and attacks except self-cast spells.
• Improved Healthstone - The increased effect from this talent should now properly apply to other players that use the Warlock's Healthstones.
• Ritual of Summoning - Fixed a bug where players could be summoned from outside the same instance as the warlock in some cases.
• Unholy Power - No longer requires the Fel Stamina talent. Is now a tier 4 talent and is a prerequisite for the new Master Demonologist talent.
• Master Conjuror - Talent replaced with a new talent called Master Demonlogist.
• New Talent (Demonology): Master Demonologist - Grants both the Warlock and the summoned demon an effect as long as that demon is active. The effect granted depends on the type of demon summoned.
• Unholy Power - No longer requires the Fel Stamina talent. It now requires the Master Demonologist talent.
• Ritual of Doom - Should now display the cooldown.

Patch 1.5.0 (7 June 2005)

• Improved Drain Mana - Damage caused is now considered Shadow damage and is no longer reduced by armor.
• Improved Voidwalker - Now increases all Voidwalker spells (now also including Sacrifice) by 10/20/30%.
• Improved Succubus - Now increases Succubus spells by 10/20/30%.
• Master Summoner - In addition to decreasing casting time of summoning the Imp, Voidwalker, Succubus and Felhunter, it now reduces mana cost by 20/40%.
• Improved Enslave Demon - In addition to reducing the attack speed and casting speed penalty of enslaved demons, it now reduces the resist chance of Enslave Demon by 2/4/6/8/10%.
• Demonic Sacrifice - Is now instant cast.
• Improved Firestone - Now also improves the bonus Fire spell damage of Firestones by 15/30%.
• Inferno - The summoned Infernal will now be enslaved for 5 minutes before turning on its summoner.
• Drain Mana - Targets with no mana will no longer be valid for Drain Mana (Rank 4), making it consistent with all other ranks of the spell.
• Improved Drain Mana - Damage caused by this talent is now improved by the Shadow Mastery talent.
• Conflagrate - Range increased.
• Siphon Life - Is now instant cast, damage increased.
• Paranoia - No longer causes threat when cast.
• War Stomp (Doomguard) - Now has a maximum of 5 targets.
• Pet speed has been increased when out of combat and following their master.
• Honorable kills will now generate a Soul Shard when Drain Soul and Shadowburn are used.
• Spirit Guides in Battlegrounds will now resurrect your last Imp, Voidwalker, Succubus or Felhunter. If the Doomguard or Infernal were the last active pet or the previous pet was killed before the Warlock, an Imp will be summoned.
• Improved Curse of Agony - Fixed a bug where Curse of Agony (rank 1) was not improved by the talent. The talent will now work properly with all ranks of Curse of Agony.

Patch 1.4.0 (20 April 2005)

• Warlock Epic Mount quest added. To begin, speak with a demon trainer in any of the capital cities: Kurgal, Martha Strain, Spackle Thornberry, or Jubahl Corpseeker.
• The Warlock Infernal quest is now available and can be found in Felwood.
• The Warlock Ritual of Doom quest is now available and can be found in the Tainted Scar.
• The succubus model has been updated.
• Paranoia (Felhunter) - Increased stealth detection.
• Seduction (Succubus) - Is now considered a Fear effect for purposes of diminishing returns.

Patch 1.3.0 (22 March 2005)

• Improved Drain Mana - Will now report to the combat log all damage caused.
• Inferno - The duration the Infernal is enslaved when first summoned has been increased. The area of effect damage caused by the Inferno spell, and all threat generated by it, will now originate from the Infernal. The Infernal will now immediately attack targets within the radius of the spell.
• Enslave Demon - Is no longer dispellable.
• Curse of Agony - Now benefits from items that increase shadow damage.
• Nightfall - Fixed a bug where the Shadow Trance effect was lost without benefit. Previously, the talent had a 3%/4% chance of triggering. It now has a 2%/4% chance of triggering, and the tooltips have been updated to accurately reflect this change.
• Ritual of Doom - The death caused at the completion of the ritual no longer causes durability loss.
• Firestone - Equipping Firestones will now increase damage caused by fire spells.
• Spellstone - Equipping Spellstones will now improve your chance to get a critical strike with spells.
• Fear - Mana cost changed to a percentage of base, which results in an increase in cost.
• The Shadow Trance buff granted by the Nightfall talent will no longer be used up by a shadowbolt that was in mid-cast.
• You can no longer accept a warlock summoning while you are in combat.
• Sorcerer Sphere and Twilight Orb are no longer Warlock only.

Patch 1.2.0 (21 December 2004)

• Warlock demons have a wide selection of names based on the demon type. This only affects new demons; existing demons will keep their names.
• Warlocks can no longer kill players in duels.
• Death Coil won't give health until it actually hits the target.
• Death Coil will only give the amount of health that it actually drained from the target.
• Create Soulstone: Reduced the Soul Shard cost from two shards to one shard.
• Curse of Shadow: Increased duration from two minutes to five minutes.
• Curse of the Elements: Increased duration from two minutes to five minutes.
• Fear: Players now have an increasing chance to break free of the effect, such that it is unlikely the effect will last more than 15 seconds.
• Devour Magic (Felhunter): Fixed a bug where the felhunter would be healed every time the spell was used, in addition to the healing gained from successful dispelling.
• Tainted Blood (Felhunter): The reactive effect no longer causes threat.
• Training costs adjusted. Total training cost was decreased.
• Enslave Demon: Can no longer be cast on tapped targets.

Patch 1.1.1 (17 November 2004)

• Inferno: Now dismisses your pet before casting to allow the Infernal to start Enslaved. Useable outdoors only.

Patch 1.1.0 (7 November 2004)

• Only party members can participate in rituals.
• Voidwalkers will wait for enemies in the area before casting Suffering.
• Target of summoning ritual must already be in the same instance if caster is in an instance.
• Summoning gives a confirmation dialog to person being summoned.
• Ghosts can no longer be summoned.
• A bug has been fixed in the calculation of total mana for Warlock pets.
• Lash of Pain (Succubus): no longer requires the succubus to be behind the target.
• Seduction (Succubus): Mana cost reduced, increased the chance of breaking early.
• Soulstones: Now soulbound when created, are consumed to store the target's soul. When that target dies, he may resurrect himself any time up until release. Cooldown added.
• Removed facing requirement from Banish, Corruption, all Curses, Enslave Demon, and Fear.
• Demon spells are now available as Grimoires from the Demon Trainers in the world. Purchase the Grimoire and read it while the appropriate demon is summoned to teach it the spell.
• Enslave Demon once again requires a soul shard, increased the chance of breaking early if cast repeatedly on the same target.
• Howl of Terror: Increased the chance of breaking early.
• Fear: Increased the chance of breaking early.
• Rain of Fire: Duration, mana cost, and damage slightly reduced, deals its damage in more frequent intervals.
• New Spell (Imp): Phase Shift (Level 12).
• New Spell: Summon Felhunter (Level 30). (Quest)
• New Spell: Inferno (Level 50). (Monster Loot)
• New Spell: Curse of Doom (Level 60).
• New Spell: Ritual of Doom (Level 60). (Monster Loot)

Beta Patch 0.12.0 (10 October 2004)

• Soothing Kiss, Suffering and Torment are now useable against targets that are immune to shadow attacks.
• Seduction now only works against Humanoids
• Banish now works against Demons and Elementals only. Cool down timer and reagent removed, duration increased, replacement added.
• Curse of Agony - Now deals its damage in three stages, damage increased, mana cost slightly increased.
• Enslave Demon - Soul Shard cost removed, duration reduced.
• Life Tap no longer interrupts mana regeneration.
• Soul Fire - Mana cost decreased.
• Sacrifice now grants the Warlock damage absorption, rather than full immunity. Duration has been increased.
• Soulstones have been changed to now resurrect the soulstone holder automatically 5 seconds after death.
• All warlock talents are now available

Beta Patch 0.11.0 (28 September 2004)

• Create Soulstone - soulstones now automatically resurrect you when you die (instead of displaying a confirmation dialog).
• Seduction now has a short cast time. Cooldown timer has been removed.
• New Spell: Curse of Shadow (Level 44).
• New Spell: Create Spellstone (Level 36).
• New Spell: Searing Pain (Level 18).
• New Spell: Soul Fire (Level 48).
• New Spell: Death Coil (Level 42).
• New Spell (Voidwalker): Suffering (Level 24).
• New Spell (Voidwalker): Consume Shadows (Level 18).
• New Spell: Howl of Terror (Level 40).
• New Spell: Create Firestone (Level 28).
• Curse of the Elements changed. It now reduces fire and frost resistances.
• Corruption duration, damage, and mana cost reduced. Deals damage much faster.
• Curse of Agony duration, damage, and mana cost reduced. Deals damage much faster.
• Hellfire duration, damage, and mana cost increased. It is now an instant cast. This spell is now quite dangerous.
• Immolate duration, damage, and mana cost reduced. Deals damage faster.
• The imp no longer runs away from melee attackers.
• You can command your imp to cancel Blood Pact.
• Most of the Warlock's Destruction and Affliction talents are now available.
• Warlock talents have been partially implemented. Two talent trees, Destruction and Affliction, are now in the game.

Beta Patch 0.10.0 (16 September 2004)

• Curse of Tongues duration has been increased.
• Curse of Weakness effect has been slightly reduced.
• Eye of Killrogg change: The eye is now stealthed, moves slower, has 1 hp, and doesn't cause aggro for the warlock if it is detected.

Beta Patch 0.9.0 (15 August 2004-08-15)

• Demon Breath renamed Unending Breath.
• Sacrificial Shield (Voidwalker) renamed Sacrifice.
• Summon Nightmare cast time decreased to be in line with other mount summoning spells.
• Nightmare renamed Felsteed.
• Felsteed no longer purchased at the trainer, but rewarded via quest.
• Found and fixed a bug that caused the cost per second of Health Funnel to be higher than it should be.
• A failed Ritual of Summoning should no longer cost a soul shard.
• Shadow Ward duration reduced, cooldown increased.
• Curse of Weakness effect reduced at higher levels.

Beta Patch 0.8.0 (7 July 2004)

• Life Drain: Renamed to Drain Life.
• Life Tap: Life Tap no longer causes threat.
• Nightmare: Getting attacked or damaged will no longer dismount the Warlock from the Nightmare.
• Siphon Mana: Renamed to Drain Mana.
• Summoned pets now regenerate at a slower rate when not in combat.