Which immediately makes me wonder how easy it would be to scale chops' site to service other MMOs. If you could get it to the point where you can release a fully-featured guild website on the launch day of each new MMO you might just be on to something :)
I should have specified that it is actually multiplatform. The site currently natively supports about 15 MMO games, and has an interface for customizing and specifying your own game parameters (level cap, tradeskills, classes, races, etc).
WoW is just the biggest player by far. Currently I host approximately 88% WoW guilds. The other "bigger players" are EQ, EQ2, Warhammer, AOC, FFXI, and LOTRO, with Warhammer being the biggest non-WoW game at 2%.