I'm not sure it works yet (I seem to recall a note Aaron made about it only recognizing that it's there, not processing it yet for playback), but the best way to test it would be to install and run trunk. Not the easiest task in the world, but once you get it set up, it's easy to stay up-to-date. Check out
http://banshee-project.org/download/development/ and
http://developer.gnome.org/tools/svn.html for some general GNOME/Banshee/SVN information and how to get up and running.
Hopefully someone else can comment specifically on what's supported now and what will be by 1.4.
Cheers,
Andrew