Just an idle thought, I've not really played with it that much. Just how does iTunes/genius know what songs go together? Is it based on what other users have got in their playlists that contain set songs? If so, can we expect the Genuis results to become better (or more diverse) over time for particular songs? Or is it more computational, looking at BPM and the "form" of the songs (however that could be calculated)...?