I am in the midst of using mp3tag 2.40 to re-organize my entire mp3 collection so that it is viewable by Zune social thanks to the new Zune market place source files. However, it is becoming quite a frustrating show stopper that mp3tag seems to choke on writing tag information for any large file/long song, the most recent being the last track from Genesis' 1972 album "Foxtrot." I've also had it choke on several Pink Floyd songs, specifically from the "Animals" and "Wish You Were Here" albums. There are many more occurances of this bug, too many to list.
The evil, non-free app, Tag&Rename, has no issues writing to these files, yet it lacks the Zune source support.