What Flickr does for pictures, TuneCircle wants to do for music libraries. I’d be more interested in seeing that kind of functionality embedded into file sharing apps than having to go to a separate environment, and the site is rather sparse at this point (at least the part you can read without creating an account).
04/06/04 update: Webjay (meets Kinja).
04/13/04 update: musiCompass, Audioscrobbler browser.
