Ted's said NO lots of times before, a big reason is because of the libel aspect. Just search for 'chat' in website feedback, I'm sure you'll find lots of treads.
Agree 110% with mungo, it has been said before, live chat will ruin the entire forum concept. The heart of ph is the help and advice that can be looked up at any time day or night. live chat would effectively remove that.
I think Teds hit the nail on the head with the two descriptions of chat room users , fortunately I can vouch that this one is a teenager. Yes he does use msn and as far as I'm concerned he can continue to do so .