Just a few notes:
1) The query to get the tagboard information slows down the loading of the profile by a lot if you have a lot of members, primarily because of the query addition to get the avatars. I removed the avatar join sections, and dropped my page loading down from 6 seconds to 0.01 seconds.
2) I changed the hack slightly to prevent members from posting in their own tagboard, and to allow staff to delete the entries as well.
Otherwise, good idea.