Think this could possibly be a bit of a bug that i've found, not sure if anyone else is suffering it or it could be confirmed that i've either gone mad or it is actually happening.
Basically:
Write a message in a guestbook and confirm it, then basically refresh and it is duplicated, if a user refreshes over and over, the message can be duplicated sever times in quick succession, which also sends a pm every time too.
I can delete guestbook messages no problem, but i;ve had to disable the guestbook featur for the moment, until I can either get a fix for this or until I am told I have gone mad.
Besides that, super hack.