Overgrow.com is a web site about marijuana cultivation and the politics and culture around it… the forums are huge. People like writing about marijuana as much as they enjoy it itself, apparently.
Don’t ask me why I know this. I know nothing! 
I would bet ebay has one of the biggest.
Well yes, because they like to talk with other marijuana fans. Thats just my opinion though. I think most drug based forums become quite popular.
I’m hoping to get my forums up there in numbers relatively soon
www.thegreenrabbit.ca
It’ll take you a few years to get in the numbers. I wish you best of luck with your goal though ;). Im not even hoping for my forum to get into the top. As i know it wont make it to the top :p. You always think of climbing one rank at a time thats how you`ll always succeed.
My Forum has over 5000 members and is very active and reached over a million page views in 60 days - www.serials2000.org
Your forum will soon be in the rankings evilive98. But im sorry to tell you page views dont really count anymore. Its all about your uniques and page views so you cant count out your uniques. But yes your forum will be in the rankings with best of the best once its a little bit older and more active 
no.
As said above its subjective, but also it depends on what is considered popular and how you quanitfy it. I.e. most posts, most members, most thread views/etc. Forums will slowly breakup as they increase, as obvious topics break to become focused forums; well thats been my observation atleast.
definately support sites and official sites have the most members.
Everything that they’ve done has been Lanzer and a few others doing custom work.
They’re also using phpbb1, not 2. And they’ll never upgrade to 2.
But yea, a site like this is simply amazing for all the features that it contains and the sheer amount of members.
However, it’s riddeled with bugs and errors. They also have something like 47 servers. But I guess you’d need that if you were to have over a million Registered Users. Do note, that several people have multiple mule accounts. So they probably only have merely 750,000 users…heh.
Are you sure of that, it seems very much like that’s phpBB2 and not 1.x… 
When was 2 released? 2002/3? Sometime around then anyways I think.
I read an interview with the creators a few months back stating that they were using 1 and would move to 2 because it’d be just too much work to change everything over.
There are two interviews with the owners of Gaia Online that talk about the technical specs of their forum at www.big-boards.com
http://www.big-boards.com/int.php?n=60
and
http://www.big-boards.com/int.php?n=60b
Cool interviews.
phpBB can handle large post counts / userbases pretty well, some of the largest (incl the largest) board on the net is run off phpBB