Mobile/desktop app combination that lets you create playlists using YouTube/Vevo videos rather than actually buying music

Everyone who has ever used the internet knows that you can almost always find a copy of the song you want to listen to on YouTube (legally sanctioned or otherwise). This app would provide an interface similar to iTunes (for example) but rather than loading up a device with actual music, it would allow a person to create playlists that simply contain links to the relevant song.