the music genome project has launched a nice web-application called pandora which reminds me of some stuff i did for my diploma thesis. they try to evaluate the user’s taste in music and build up a radio station which will only play songs of bands that the user likes most.
you only have to give them your favourite band and rank
recommended songs of other bands, which they think you might like.
it would be interesting to know, if they used some kind of collaborative filtering, which became quite popular by the recommender engine of amazon.com. i was pleasantly surprised that pandora works really well!