Yesterday World of Warcraft recieved several hotfixes that changed the mechanics of bosses in Icecrown Citadel and Vault of Archavon:

• Blood Queen Lana’thel will now begin her flight phase a little earlier in 25 player mode, Vampiric Bite is no longer mitigated by armor, and the damage of Vampiric Bite has been reduced.
• Toravon will now be affected appropriately by Area-of-Effect damage spells.
• The Frost Orb corpses in the Toravon encounter will now despawn faster.
• Players who are dead will now get credit as intended when defeating the Valithria Dreamwalker encounter.
• Players can no longer zone in while the Valithria Dreamwalker encounter is active.
• Anti Magic Shell no longer resets the Mystic Buffet stacks in the Sindragosa encounter.
• The Val’kyr in the Lich King encounter are no longer affected by Death Grip and will head to ledges faster.

This was followed by an emergency hotfix that changed how certain Engineering explosives behaved in order to address the Lich King fight exploit:

We just made a hotfix that disables the siege damage dealt by Saronite Bombs and the Global Thermal Sapper Charge. The siege damage of the bombs was causing the Frozen Throne platform to rebuild, which greatly decreases the difficulty of the encounter.

We'll reenable the siege damage in a later update when the issue with the Frozen Throne is fixed.

Late last night a third fix was implemented that reverted the previous change to the
Deathbringer Saurfang encounter:

We've just deployed a hotfix that reduces Saurfang's blood power gain from ability damage back to 3.3.0 values. There was also a minor visual range issue with Blood Nova that was fixed.

The Saurfang encounter was initially changed in an attempt to prevent the now-common strategy of allowing players that recieve Mark of the Fallen Champion to die, thereby reducing the healing load on the raid and decreasing his blood power gain significantly. The change seemed to have gone overboard, however, as Saurfang began recieving massive amounts of blood power making the fight much more difficult than Blizzard intended.

The Queen Lana'thel change addresses the phenomenon where the Vampiric Bite would sync up with the Queen's Fear and Bloodbolt Whirl which could lead to unmanageable situations depending on luck. This will make the first flight phase, and the rest of the encounter significantly less random and much easier to beat.