The backups did, indeed, work, though the /etc/ backup wasn't quite as recent as I'd have liked.  However, now *another* disk is corrupting (this time the home/var disk), and it looks like it's the motherboard's SATA controller at fault.  Replacing that will require new motherboard, memory, and CPU... and yet another day of working on it instead of the dozens of tasks on my todo list.  Going to have to shut down the machine until I get the parts and the time to fix it.

[Update] Motherboard + CPU + Memory *or* buy a PCI SATA card for $50... I am tempted...