As in a shoutbox? Nah. If I had wanted to chat, I'd rather go on IRC or some place else. It would defeat the purpose of a forum altogether. But the fireplace idea is nice.
a Hi, Bye, Leave msg thread will be ok althought what is the "To clear" rate (number of back posting allowable) is the crux since there's only a certain amount a thread can hold before it lags to infinity.