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?
