It sounds like the same thing Last.fm provides.   

As their web page says, "Last.fm rocks! It also boogies, raps, jives, shakes its booty, and sings opera. All at once, in a high-quality (128kbps) MP3 stream. Welcome to personalized radio, where the DJ is a computer that picks the best songs to play you. You can skip songs you don't like, and your musical profile updates accordingly. All you need to tune in is the Last.fm Player, a small, free, open source application that connects to our network to play music just for you."

It takes about three to five hundred songs played before the software comes up with truly 'personalized' radio for you, and then there is a 'small fee' (3 euros/US dollars a month) to access that one-click link (eg "Bard Judith's Radio Station"). However, you can use the 'Play Music Like' feature completely free twenty-four hours a day - just type in a few names and it will start up, heavily weighed with the artists you've actually chosen but branching out even across genres to provide interesting listening. There are two or three inconspicuous hypertext advertisements - but who looks at a music page, right? It's always windowed in the background while you do something else! I know I'm really enjoying it and have discovered all kinds of names and sounds I never would have otherwise.

Note that despite the 'plug' above I haven't conveniently provided a blue clicky, so you know I'm a real person with my own musical tastes and not an advertising magnate from Last.fm... :) I shall, however, go have a look at Pandora and let you know how it compares....