Just needed to copy my Rhythmbox ratings from one machine to another. So, a quick script to do it: rhythmbox-ratings-export.py. It assumes that all your mp3s are at the same path on both machines, which is fine for me because they are (my music folder is in Ubuntu One), and it’s basically very stupid and venial and you shouldn’t do it this way. But it worked when I needed to quickly transfer a bunch of ratings and was prepared to ponce about on the command line, so someone else might find it useful.
Memo to self: write plugin to sync this stuff properly.