Pandora is an online, user-customizable radio station that is built from data from the Music Genome Project.
Pandora Radio is an automated music recommendation service and custodian of the Music Genome Project. Users enter a song or artist that they enjoy, and the service responds by playing selections that are musically similar. Users provide feedback on approval or disapproval of individual songs, which Pandora takes into account for future selections.
See Pandora website: http://www.pandora.com/about