Thanks to the intelligent answers on here + Google, I've learned a ton about Pulse Audio. I think my immediate short-term solution will be a Zune HD (since it now supports xvid).

The longer-term solution is to wait.

And - to all those whose tags are messed up - the best solution is http://www.mp3tag.de/en/.

I have zero problems with artwork and tags in my N900 media player. Give it a shot, it works great and is free!