"Audioscrobbler is a computer system that builds up a detailed profile of your musical taste. After installing an Audioscrobbler Plugin, your computer sends the name of every song you play to the Audioscrobbler Server....With this information, Audioscrobbler is able to automatically generate suggestions for new songs/artists you might like."
I haven't tried it, but sounds interesting. You'd think for a music-related thing, it'd have a less awkward-wounding name. (Also sounds a lot like something else.)