A friend just suggested this program, and it's quite impressive.
One feature I would really like to see however would be a way to toggle what type of tag you are looking at. Say for instance that the mp3 file has both id3v1 and id3v2 comments in it and you wanted to make sure they were both set to what you want in the tag, having a button to be able to toggle which tag type you were veiwing would be very useful!
Tag & Rename has this feature, if you wanted to get an idea of what I am talking about. But I must say I really prefer mp3tag to that other program!