Goombah

Goombah interacts with iTunes to help users discover new music, rediscover old favorites, and download free tracks based on their taste.

Goombah analyzes each member's iTunes collection and displays their closest matching members and their libraries. For each user, it recommends tracks that their matching members really like that are not in the user's collection. Goombah (beta) has more than 3 million tracks in their members' collections from which to draw recommendations.
If you have a previous release of Goombah, you may see a "The file is in use" message when you try to copy the new Goombah over the old one. Simply drag the old version into the Trash and then copy the new version into the Applications folder. The old one can then be deleted after you log on the next time.