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.