In the process of moving the data from the old LVM array to the new RAID array, I noticed a lot of "file disappeared" or other bad I/O-type errors. Upon further investigation it looked like one of my 120G drives was dying in the old array.
Eventually the drive started beeping. Yes - beeping. That is, beeping in between evil grinding sounds. And like the other 40G drive, it stopped responding to SMART commands.
Just from occasional glimpses as the copy was running, it looked like it was mostly movies and other TV episodes that I lost, but I'll never know for certain without the file list. Hopefully this ends the "week of hardware failure".