Well, for me, anyway. Moe has been around for several years and far be it from me to predict when it’ll end, but for me it died while reading vol. two of Kakifly’s K-On!
I don’t think K-On! itself caused it; I did like the first season of the anime adaptation, though I never watched season two. Rather, while about halfway through the graphic novel, I realised that I just didn’t care about this story. I think the sudden realisation may stem from a recent episode of the ANNcast podcast, where one of the co-hosts (Justin Zevakis, IIRC) commented that, as a grown man, he had no reason to care about what a group of high school girls are doing.
Actually, maybe my distaste isn’t with moe per se, but with high school comedies. The first graphic novel I really got into was Azumanga Daioh, by Azuma Kiyohiko. At the time, I was in high school, so watching a bunch of high schoolers was relevant to my interests, even (or perhaps especially) if they were girls. Since then, though, I’ve seen several other shows with the same setting, some of which I’m sure I’ll still like, but at this point I graduated high school five years ago. The setting seems really trivial, and honestly some stories suffer from the lack of gravity inherent in most teenage relationships. ToraDora had this problem – though the urgency the characters felt to clarify everyone’s feelings may have seemed important from their point of view, I found that sense of urgency unnecessary.