K-On!'s "model school" (presumably the school upon which they based the school in the show, design-wise) is happily lapping up the attention they get from the connection: they hosted a concert featuring four girls cosplaying as Mio, Ritsu, Tsumugi, and Yui.
The concert featured themes from the show, of course, and it sounds like the cosplayers did an okay job (although the hardcore K-On! fans, like those at Zone Otaku, will note that the Mio cosplayer isn't left-handed like the character-- still, that's tough to find).
The school also held a "K-On! Cafe" in one of their classrooms, complete with a chalkboard for visitors to leave messages on. [ Via Zone Otaku.]
There are a good handful of anime that revolve around music on some level-- Beck, K-On!, Nodame Cantabile, etc. What show would you most want to see in concert, theoretically?