One thing that has always annoyed massively is that all my ratings get lost when I reinstall my system. And that happens often.
I know from MediaMonkey for Windows that it is possible to write the rating to tags. Interestingly, when loading the songs into Banshee, for instance, the ratings are recognized in fact!
But apparently, Banshee does not write ratings to the ID3 tag itself. Which player is capable of that?
Banshee can do this, but you first need to go to Edit->Preferences and tick the checkbox labelled "Write ratings and play counts to files".
Also - Quod Libet can (optionally) save ratings into many audio formats.