
"Using a music recommender system called "Audioscrobbler", Last.fm builds a detailed profile of each user's musical taste by recording details of the songs the user listens to, either from Internet radio stations, or the user's computer or many portable music devices. This information is transferred to Last.fm's database ("scrobbled") either via the music player itself (Rdio, Spotify, Amarok) or via a plugin installed into the user's music player. The profile data is then displayed on the user's profile page. The site offers numerous social networking features and can recommend and play artists similar to the user's favourites."
if ya dunt have it i highly recommend signing up, its 100% free, and we'll get U2's numbers up a bit
