Some stuff is clear cut. If you own pretty much all the CDs (or mp3s, as the case may be) for a band its pretty clear cut you're a fan. Or if you've intentionally seen then a bunch of times in concert. But I'm not a big concert go-er so that's not much of a criteria. And there are only a few bands that I own more than 2 CDs by them. Some bands are particularly odd for me, like Jimmy Buffett or U2 or Foo Fighters. I like a bunch of their songs but don't like a single one of their CDs. In the case of the Foo Fighters in particular, I like all their songs I've ever heard on the radio but I've listened to all their CDs and dislike everything else they've ever done.
And is there anyone who doesn't think that this is a ridicously overanalyzed and nitpicky meaningless question on my part? I geniunely want to know the answer but I also feel somehow foolish for needing some kind of guideline for defining my level of fandom/like of something.