I used to run a similar service called Audio Vine. You'd start by picking one song. Then you were given 4 choices for the next song, which were derived from L

I used to run a similar service called Audio Vine. You'd start by picking one song. Then you were given 4 choices for the next song, which were derived from Last.fm's "similar song" API. If you didn't make a selection by the end of the song, one of the four options were chosen at random. It ended up being a very pleasant experience, a semi-randomized radio that gave the user the ability to steer the direction. The service also ended up producing this neat tree graph (done in D3) in which you could go back and traverse unexplored nodes. We had an agreement with Grooveshark to stream from their music database, so unfortunately, when they went down, so did Audio Vine. But man, that was a fun project.