This evening the site went potty and stopped displaying all but the admin pages. After several hair pulling sessions I enlisted the help of the server admin, who couldn't find any error logs about it (blank pages normally mean suppressed errors) - so he started pulling his hair out.
We ended up restoring the DB and files from the last update which was about 20 hours ago. We found the current DB wasn't causing the error - so thankfully we didn't lose any posts or this new forum made this morning. What we did lose is the modified BBCode FAQ (which was the original cause of the 21/9 meltdown) - but I doubt anyone's noticed it was changed in the first place.

I apologise for any inconvenience made to authors and testers as the site was inactive for the last 5 hours.
Enjoy the new spoiler tag