On my forum (http://www.astralsociety.us/index.php?action=forum) running 2.0 RC1 all of my post with the exception of stickied topics have vanished. All members, post count, board names, categories and so on are still intact. I was wondering if anyone had any idea how such thing might have taken place. I have not made any changes to the site prior to this happening. The only mod I had installed was simple portal.
Do you have a recent backup? If so, try restoring back to that backup and see if your posts come back.