This app is still raw, and I ain’t saying it’s going to take over the world or nothing. But this seems like the time to point out that the XSPF architectural principle of separating specific files from song references has turned out to be very durable. We originally conceived of it as an issue of matching up references to shared playlists with MP3s in your local stash, and I don’t know how crucial this feature is. But the important idea is that sharing taste in a world where every file isn’t shared means passing around identifiers rather than files, then resolving the identifiers to files at playback time, in the context of the listener’s music acquisition resources. At that level of abstraction cloud-based catalogs like Rhapsody, Spotify, YouTube and Seeqpod can do a lot of useful things.