Over approximately the last five days (starting on Jan 4, 2009), the database backing the message board was corrupted. I believe this corruption occurred on Jan 4, as a side effect of running out of space on the tmp partition of the server.
MySQL can recover corrupted databases, but the process is lengthy. After letting the recovery process run for the last four days, I realized that all statistics indicated that the recovery could potentially take weeks given the enormous size of the database that back the message board. (It's over 1GB total, with multiple millions of rows of sorted data--sorting is the typical technique used to recover the DB tables.)
Rather than spending a month to try to save 5 days worth of posts (while simultaneously making the boards unavailable for posts), I decided to restore from a recent DB backup. The backup was created on 12/31. Any posts or other actions that were taken after 12/31 are GONE.
This includes a post I made indicating that I believed I had fixed some of the database errors that were slowing down the forums. I still believe that I have fixed those errors, and that the multi-day day downtime that we experienced was a result of filling up the tmp directory as part of that investigation.
Please report any database errors or other problems that you experience, other than lost posts from the last 5 days.