iTunes used to be an awesome way to manage your listening to music. You could create Smart Playlists that would play on your iOS device. The awesome thing was that it could keep track of Play Date and thus give you songs you hadn't heard in time period X. Now iTunes still works this way if you are on the Mac desktop, but all of these features are broken for correctly syncing this playlist to an iOS device.
Dropbox allows one to upload a bunch of MP3 files and then play them. It wouldn't take too much more coding to make some play counts, last played dates, and then Smart Playlists. You all seem to be chomping at the bit to expand the utility of DB: music would be awesome. Nothing on the market like it now, I can attest!