I generally avoid the mainstream in music these days. I find that most of it is either, borderline monotone droning with an added beat or just completely uninspiring. Most of the music I listen to is either somewhat less mainstream or fairly old.
I think a lot of older songs seem to age better as well. Most pop songs seem to last a month or two on the charts and are simply forgotten.
Usually I'm not so open about these opinions, because I imagine that the vast majority of people would refer to someone who doesn't like mainstream music as an "Indie" Wanker or something. I don't think that's quite fair. It is, however, fair to say that to someone who listens to non-mainstream music because they think it's 'cool' or 'hip' and whatnot. I avoid listening to pop music because it's shit.