Probably not useful for a lot of persons, but I still give the idea:

you have a desktop and a laptop. Most of your songs are on your desktop, all
rated, with all the settings you like. You just transfer a few songs on your
laptop from time to time for travels, whatever. Then you will miss your settings
and rating on the laptop. It would be specially useful if/when there are
"advanced" playlists in Banshee. Like "top 20 U2 songs", it requires advanced
playlist using ratings. 

Would be perfect if I could transfer the ratings and more generally the settings
on the laptop. 

This could be extended later to a "server" functionnality. You can configure the
desktop banshee to be a "server", then from the laptop you specify the IP of the
server, and you can download songs from the server. On the server you can also
see the clients just like Ipods. It would transfer the ratings at the same time.