Just thought I would give last.fm a plug.
For those of you who haven't discovered its delights last.fm lets you do all sorts of cool things with music from tracking and charting your listening in iTunes to building channels of your favourites, friends listening and neighbours online. I first played with it ages ago when it was in beta, and in fact arranged for the guys to come in and do a workshop when I was at the Beeb, but I'd got frustrated with the functionality and reliability in those days and wandered off to Pandora.
Well I have to say I am glad I am back. The personal radio channel last.fm has created round my tags is more accurate than Pandora's, I love being able to share my "favourited "tracks and there is so much more in terms of patterns and interesting connections with other users.