I had been given a hack a while ago, but I can't find it in my mail, and I'm not sure how it would have been added to the new 5.0.6 or if that would have mattered or not (having used it on 5.0.5). It was for the list template or php, I can't remember, and it showed e-mail address people entered if not a registered user for "last post by". I noticed that in the 'loast post by' column, the only names with links are the ones to profiles.