Pandora is deceptively simple. For free, members can create any number of radio stations based on the sounds of a favorite song or artist, such as "Blackbird" by the Beatles or just the music of Prince. Once the artist or song is found in the system, the station streams from the Web, within seconds, music that is rhythmically or artistically similar. Because of licensing restrictions, Pandora does not play any one song on demand. People can give a newly played song a "thumbs up" or "thumbs down" to tailor future selections, or they can request a new song or artist to add diversity.