I was scanning the boards to look for an old post, and it seems like there's less threads than there should be. Are the forums set to wipe posts/threads after they get too old? That would be a total bummer... this place is like a living archive of knowledge... it'd be horrible to have it just wiped clean.
Hmm, I checked on the config and the "pruning" was enabled. It doesn't say how old a post had to be to be "pruned" though. I disabled it. I see at least the 'welcome' thread on the general board is still here, from Oct. 2004.
After a bit of Google detective work, it appears phpBB's pruning code makes a decision based on the date of the last post in a topic.