Or use Rdio? I've never been impressed with Spotify. The experience on Rdio has been great for me.
But, I almost exclusively use http://www.grooveshark.com and http://www.songza.com
Both are web based, the latter has a mobile app, both absolutely brilliant and FREE! I'll have to check out Rdio, that looks real interesting.
All in all, I just didn't find the service that interesting unless you consider the technological angle.
All in all, I guess it might work for some people. It just didn't make the cut for me. For that matter, neither did Spotify or Pandora. I guess I'm just not the target audience for that kind of service in general.