While taking a break from life today, I found a link to another site called Pandora.
References to a Music Genome Project make it sound very cool in what they are trying to do.
I just signed up for my free account and have been listening for the last 30 minutes. The music has been quite random, though the choices I made in my personal station are clear in the genre of music being offered to me.
I have not seen any of the advertising that was warned about in the sign up procedure unless you count the advertising on the right hand side oft he page - which I consider to be non-obtrusive anyway.