According to Tigole, a hotfix to the Lady Vashj encounter (the final encounter in Serpentshrine Cavern) should go live on US realms in the next 24 hours -- presumably during this Tuesday's maintenance, though Tigole doesn't specify. Specifically, the hotfix should adjust the amount of hitpoints some of the add spawns have.
With only three guilds up to Lady Vash so far, this hotfix sets up some real competition. MMO-CHAMPION makes the reasonable speculation that if the hotfix requires downtime US guild Death & Taxes will likely get the world first kill, because US maintenance comes before EU maintenance. But if it's a hotfix requiring no downtime (that may have even gone live already), EU guilds Curse and Nihilum will have extra time to work on the encounter before their instance resets, giving one of them the world first. So who's going to win this race? If I don't see a first kill announcement somewhere in the next 24 hours, I'll be greatly surprised.