Mine is pretty big, not huge though. Probably the smallest of those listed on this thread, actually.
http://www.nightly.net around 14,000 members, around half million posts, and 200+ daily active topics
Now if you want to see a HUGE message board...well then look here:
http://boards.theforce.net/ It isn't a UBB, but it's ginormous. 12 million posts, 115,000 members, 5000 active daily topics, 250 forums.
