save song-ratings in mp3 metatags
Sometimes you have some music in your download folder or on a temporary net mount and you listen to it with Amarok and give them ratings. Then you move/copy these files to your music directory and all ratings disappear. Or you remanage your music directory, rename some folders, move an album from Rock to Metal, whatever, in all cases, all ratings disappear.
Another possibility would be to store all ratings in a database which relates each rating to the song-name or the song-content, but not to the absolute filename.