I've been a Rhapsody subscriber since 2003. Although it was one of the earliest music streaming services, it never really got a lot of attention. Lately, though, a bunch of new services like Rdio and Spotify have been getting a lot of attention and new subscribers.

One advantage of on-demand music streaming services like Rhapsody, Rdio, MOG, Spotify, etc is that monthly subscriptions means there's no investment to lose if you decide later to switch to another service. However, one thing you do have stored with the service that you'd have to give up if you left is your personal library of tracks, playlists, and ratings. Since all the services store similar information, why doesn't there yet exist a tool to allow you to copy your library and playlists from one services to another, not by actually copying any music but by automatically setting up identical playlists from the new service's catalog.

Along with this functionality comes another incredibly useful feature. When deciding between music streaming services one of the prime points of comparison is the size and makeup of the catalogs. Comparing these things in general is tricky with reviews saying things like "service A has the biggest collection, while service B's somewhat smaller collection is still pretty large but with certain glaring holes." Without them specifying what these holes are, I have no idea if they would be a deal-breaker for me or not. However, as an existing subscriber of one of the competitors, there is a very straightforward way of showing me whether the catalog gaps would be significant to me. Any tool that could migrate my library from one service to another could also do a side-by-side comparison of potential new services to my existing service by showing me which tracks from my existing library I would lose after the transition.