Taking a gander at the official forums tonight will reveal something magically spooky.
All the blue posters have been turned into glowing jack-o-lanterns, and all of us normal folks have turned into undead zombies.
The conspiracy theorist in me suggests that this is a clue to the next stage of the zombie invasion. Tomorrow we'll all log on and have a strange urge for brains and only brains. Lots and lots of juicy... yummy... braaains. Insert Homer Simpson drool here.
Of course this could just be another fancy bit for Halloween, but who knows....
There is no indication how long this will last, and also there's no word if there'll be new Wrath of the Lich King avatars after this is done as there were when the Burning Crusade was released.