I've been using last.fm since it was audioscrobbler. I wrote one of the mac scrobblers years ago to upload my iPod plays. While it is fun to track my analytics, its user recommender is poor at best and the radio, I don't know, it just doesn't match my taste. I use it all the time to find popular songs by artists I've just discovered though. Great for evaluation.

Sharemyplaylist.com is basically what makes Spotify useful for me at all. I still can't talk to anyone, but at least I can have a playlist that sounds roughly like the songs belong together. I'll rarely discover new music on it.

For music discovery, I find http://hypem.com and mp3 blogs to be far more useful. Still no strong community, but at least I actually discover new interesting things.