I’ve been a fairly regular poster since 2001 and I haven’t noticed any format change. Maybe a change of topics or topic-organization. I don’t know. I don’t pay much attention to that. But the actual format of the site itself, the way the threads list out, it hasn’t changed as far as I remember. And for what it’s worth, I think it’s the best forum format on the internet.
There was a sort of “shell” applied in I believe early 2008 that prettied up the formatting. A few features disappeared, the polls, the thread hit count.