Shana pointed out earlier today that my website wasn't up and running, so I dropped by my house to check it out over lunch. Rebooting the server failed to clear the problem, so I hooked up a monitor to the machine to see the console messages, and saw the dreaded message:
DISK BOOT FAILURE
This almost certainly means a disk crash and loss of unknown amounts of data; disk crashes on modern drives are depressingly fatal. The server had two disks in it, so it's not clear what was on the failed disk; recovery efforts will start some time this weekend.