TSP was right at the time he posted. Currently, teh server apparently is having issues--woke up this morning and the machine had restarted itself (power outtage, apparently), and now Minecraft won't start. Working on it.
---------- Post added at 13:55 ---------- Previous post was at 13:46 ----------
The world file was apparently corrupted when the server went down. I've restored the previous backup (10/22/2011 00:00:00, PST), which means the server "rolled back" by 12-16 hours (no way of telling for sure).
Apologies to anyone who lost anything. As far as I can tell there's no way to figure out what went wrong here, but I can increase the backup cadence from 24 hours to 12 (or 6) hours if this happens again.
---------- Post added at 14:26 ---------- Previous post was at 13:55 ----------
Apparently the Minecraft auth servers are currently down again/still:
http://www.isminecraftdown.net/