For me, it's been very gradual. I don't think it would have occured to me not to call myself a feminist as a teenager, but it also wasn't really on my radar. I also went through the 'yay, empowerfullisement, post-feminism' stage at university.
I think now my stance is fairly radical (and I think MN is very radical in some ways, eg., the lack of tolerance for rape myths at least in FWR, and the awareness of a need for women-only space). I know that I have to tone things down to explain anything to my family, which is a bit sad. But it all makes me more and more aware we really do need feminism. I don't know how much that's because sexism is more overt now than it was a few years ago, and how much it's because there's finally a backlash against diluted fun-feminism.
Anyway, discussing this on the pub, justtherightbullets and I figured a thread might be nice, to talk about how we became aware of feminism.