As happens with practically every large content patch, a few posts outlining unannounced changes have sprung up, giving us an idea of the things Blizzard either didn't notice or tried to sneak by us. You can find the actual forum post here, while WoWWiki has a post up with some of them, but it's a bit outdated. Keep checking back as new information crops up! The most important reported change so far has to do with a bug regarding the addition of Badges of Justice to chests in dungeons:

# The Vazruden/Nazan chest in Heroic Hellfire Ramparts is bugged.

If all the item rolls are decided and the chest becomes "empty", the chest despawns. People who didn't opened it before all the rolls got decided won't be able to loot their Badges of Justice.

Oh and I hear Onyxia Deep Breaths more. Just FYI. =P