Audioscrobbler

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, the Audioscrobbler server builds you a ‘Musical Profile’. Statistics from your Musical Profile are shown on your Audioscrobbler User Page, available for everyone to view.

http://www.audioscrobbler.com/