Better Tag Support?

Support all of iTunes basic tags on the Get Info tab (such as Grouping etc.) Or even better, support MP4 files as well. I store my ratings under the Grouping tag as I don't use it for anything else, and it's nice to have it stored on the file... and I'd like to do the same with Songbird!
P.S. Thanks for all the hard work and the best Jukebox on Linux!