Audioscrobbler is a plugin for WinAmp and XMMS that collects your listening behavior and aggregates it online along with other users. With data on what people are listening to, the system could begin to connect people to each other, users to new music they’re unaware of, or make predictions on the popularity of a given artist or song.
Unfortunately, the service has yet to reach critical mass (it only has 83 subscribed users), but it appears to be growing slowly. Even with a limited amount of raw data, its experimental artist similarity system pulls out pretty good predictions: a search for slowdive returns Sigur Ros, Mahogany, Bowery Electric and Mogwai, among others.
I’d love to see it grow, and I’d love to get my hands on the data. Mmmm… data.