Discovered Blip.fm today. Here you can tweet music you like and add comments. Yes, tweet, because it's basicly a copy of Twitter, but centered on music. It's pretty good, as all tracks can actually be played and you can create complete playlists.

I do have my questions about the legality of it all, because most of these songs are not hosted by Blip.fm themselves. Users can add songs by pointing to a URL, where the MP3 file resides. Naturally you should only do that to songs that are hosted with permission of the original copyright holders. Well, I think you know what's the score on that one. Anyway, try it out and enjoy it while it lasts. It really has potential. Here's my personal profile on Blip.fm