I just added a DO_FACTORY_RESTORE file to USB storage, and noticed that it created a system folder while I was typing the previous message. Time to eject and reboot -- AFTER I see what files I can unerase on the shared vfat partition.
My unerase program shows that the kindle is shared as an MBR device, with one partition. That means that we should indeed be able to repartion it into multiple partitions, such as vfat AND ext3 (or more) and they should all get shared to the host PC. That could be very useful.
Hmm. Thorough scan, and no erased documents. Either a full (slow) format, or this device never had any content other than the default files. Time to reboot so it can do a factory restore (just because...).