rushing, ad infinitum
I discover music a load of different ways, though the most prevalent is through other people's recommendations. For instance, on another forum, a member's username is Mogwai, and I was curious as to what it meant. He told me that it was the Scottish post-rock band. I tried it out (via Youtube, since internet radios suck and don't play post-rock music right o h m y g o d) and loved it, and was, from that point, a fan of post-rock music with the discovery of other bands in the same genre, etc.
I never discover new genres/artists via Youtube because when I use Youtube I end up watching specific video series' or listening to specific artists/watching specific videos. Honestly, I can't think of a time I've legitimately browsed the site for new things. I'm usually referred to things or I happen to stumble upon a genre/artist on a site or wiki.