I would think that in approaching this you need to look at why this forum was created. Which is to help out users control their big boards.

Based on that I would say based on my experience, I didn't start noticing some issues until I received 1 1/4 million posts and about 200 users online at a time. Things started to slow down.

So I think any condition in which you have a large number of posts or users and your forum is not performing as you think it should, and need some assistance in improving the speed or reliablity of you forum you should be able to post here.

Now obviously someone with 75K posts and 200 users probably needs not apply. ;)

I think it should not be measured by # of posts/users/etc.

More in the line of server power needed/number of servers needed.

Just to feed this discussion a bit more. :D

If you want to be concidered on the BIGBOARDS site you need a min. of 250,000 posts.

I also hope we can use this section to discuss how certain plugins/mods might affect a large forum's performance.

-vissa

I think 50K users is way too many. We only have about 16K users, but just under 700,000 posts and most days see 600 to 800+ users online during the evening peak (our max is 1080 set this week).

That is incorrect.
Unless a forum has 500k posts, it's not a Big Board. That's the definition commonly accepted by those who are running large forums, I don't see how creating a different definition would serve any purpose other than be an ego booster for those with 80k posts who want to call themselves a big board.

Everybody considers 500,000 posts a big board but is it really that big?

I've had my boards up since August 20th... have just under 1800 members and 380, 000 posts.... and my board isn't nowhere near big...

although the main measure is total posts, id look at online users and new posts per day as more "accurate" measures

although my board is small, in 6 months its rose from 50 posts per day to 200 posts per day and growing

Well Big-Boards.com defines big as 500,000 + posts:

http://www.big-boards.com/submit/

I'd say 2000+ active members would define a big board.. but that's just my small thinking :D