Not really the most IMO is gaiaonline.com, filled with prepubescent kids with nothing to do and useless comments and spam promoted posts filled with some net junkie and very loyal people, I think that is the place where databases are being pushed to the limit.
OMG Gia board (or whatever it is) has 896069176 *(posts) 5607293 (users) That's just ...... (no comments) But I think they should get a better server DP isn't the most populated forum but it is the best (well managed)
Yeah this forum isn't the biggest but it is my favourite out of all the other webmaster forums i go to (like sitepoint, namepros, webmaster world, etc)