You have to kill at least 31 bosses in Icecrown while WoW power leveling.
Ghostcrawler has posted an interesting little hint at the next patch (we know of) headed to the game. In response to a discussion about "tanking niches," he talks about Icecrown Citadel over on the forums, and just happens to mention that people might think of tanks as waiting outside until "boss 4, 17 and 31 (yes, IC is that big)." 31 bosses? More like Icecrowded, am I right?
Blackrock Depths is the largest 5-man in the game, if not the largest instance, and it boasts over 40 bosses (that's mostly counting encounters, though -- you wouldn't count The Seven, for example, as seven different bosses), including lots and lots of optional bosses and even a holiday boss. Ulduar, by comparison, has about 14, and Karazhan is about that same size (though that depends on how you count random bosses, like the Opera Event). No matter how you slice it, 31 raid bosses is a ton of bosses to go through -- Icecrown could be a return to a really epic, large-scale instance. Those skilled players can wait to experience the World of Warcraft Power Leveling to show themselves.
Of course, there will likely be wings involved (Naxxramas' Quarters have worked out pretty well, I think), and with the new changes to raid lockouts, Blizzard no longer needs to squeeze the raiding experience into an average of two or three nights a week (which is what it seemed like they were usually aiming for before). If yours is the kind of guild that likes to clear everything in one night, though, you might want to start freeing up some time now.