They're no "guest" as such - they're going through the registration, doing the email confirmation, whole 9 yards ... I'm hoping for some kind of "distributed spam-word list" on the new software that would take care of these kind of posts ... maybe do as if at accepted the post, then turn around and delete both the poster and the post a couple seconds later ...
For now, I just keep deleting these a-holes and banning their email domains from being used for registering ...