Oh, I see, I've got it to work now. I was just clicking "add to playlist" and nothing was happening, but if you click on the name of the song it starts playing.
In which case, very impressive. I'm particularly impressed that it even finds mashups, and the interface (apart from the difficulty I had with getting it to play) is very nice.
I hope you've thought through the legal issues. It could really use a FAQ with answers to questions like "So where the hell is all this music coming from?"
Further comment (because I've continued to play with it, because I think it's awesome):
I've found a couple of tracks where the time (in green on the right as it plays) was given as "NaN:NaN". That's probably not a desired behaviour. (fwiw the track was "Thunderbirds Are Coming Out" by TISM)
