http://www.audioscrobbler.com/

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.

There are lots of people using Audioscrobbler, but you probably won’t be interested in most of them. The Audioscrobbler Server calculates which people are most similar to you, based on shared musical taste, so you can take a look at what your peers are listening to. With this information, Audioscrobbler is able to automatically generate suggestions for new songs/artists you might like. These suggestions are based on the same principles as Amazon’s «People who bought this also bought X,Y,Z», but because the Audioscrobbler data is what people are actually listening to, the suggestions tend to make more sense than Amazon. It’s not just pure statistics and recommendations, there are active forums, groups, weekly charts… The system is being worked on full time, and we plan to roll out many more exciting features.

Audioscrobbler is designed to be as transparent as possible. This means that once you have installed an Audioscrobbler plugin, you don’t have to do anything. Audioscrobbler will never irritate you by asking you to rate songs, asking you what mood you are in or anything else like that. All it cares about is which songs you play.

Audioscrobbler plugins are all Open Source. We’re not keeping the data to ourselves either: Anonymous Audioscrobbler listening data is released under a Creative Commons License. This license means anyone is free to download and experiment with the data, but may not use it for commercial purposes.

Any time you feel like it, you can come to the website and check out your profile, perhaps try some of the suggested songs, see the suggestions from other similar people and generally marvel at what appalling music taste many people have compared to you.