I've never implemented any message-board software, but I there's been some discussion recently at Home Theater Forum .com .
Basically, they were using UBB and didn't like it. So they switched to V-Bulletin. They like it even less and are going back to UBB. They are hobbyists, with about 100,000 hits/day, and can't afford to upgrade hardware to get the forum code to work well.
Here's a quote from their comments:
"Nearly 1 month ago, we upgraded to V-BULLETIN software. We had hoped this software would improve our overall performance.
We are a forum that gets read by 100,000 people PER DAY and an average of 550 new signups per month (that we approve). The strain on our forum during peak hours far exceeds what the software can handle.
V-BULLETIN is just not doing the job. As rotten as UBB was, V-BULLETIN has caused even more problems. This does not just include forum access speed, but all sorts of display problems for our members using AOL, WebTV, and older versions of popular browsers.
On Tuesday May 8th, we will revert back to UBB software and just stick with it until something better comes along."