Just found this new N9 app to edit mp3 meta data. Haven't tried it yet to see if it can also embed album art, but it looks very promising!

http://my-meego.com/software/applica...Auto=778&faq=2


EDIT: Just checked, not only does this new app not allow adding album art, but it does not even recognized art that has already been embedded into the mp3 file's meta data.