Thanks guys except for Tdubbs. Sounds like a great service. I think the ADD risk would be more than offset by the benefit of getting more similar artist-type recommendations than I do now (instead of downloading yet another Lifehouse album maybe I could find some more similar bands).
I've heard MOG is very similar, according to
this it's superior in every way minus the social networking part.
According to
this, which reviews all of them, Spotify and MOG come out on top.