I agree, I woke up one morning and walked into the front room, dd(4) was dying to tell me that "Daddies been on Mumsnet" lol. Love the fact that dd grassed him up, his explanation was that the thread was open from last night (it wasn't) and he'd had a quick skim .
I'm not really that bothered that I'd start an argument, but I am tempted to leave cryptic messages just in case he is watching (BigBrother emoticon)