Musicstrands [disclosure: I company I work externally for] is also working on music recommendation technology, but based on «what the user plays», with good results. Then it combines the information with other users' lists and a giant database of songs and records. MusicStrands gets the «playcounts» from your iPod/iTunes, or you can upload your song lists. This is not the same than «tell us what do you like» or «what you have bought» but a more realistic approach. People interested in this kind of technologies may want to take a look.