MP3TAG is a GREAT tool. A few ideas...
you can not select multiple items in the "add directory" dialog box. Adding to that annoyance is the "Add Dir" item has no menu-key or hot-key, so you must mouse around a lot to bring it up.
likewise, drag and drop from the desktop does not support multiple items.
finally, a method for finding/converting "special characters" (diacriticals, or 8-bit) would be nice (or an ASCII-ONLY conversion)