When my computer came back on, I had no network. Not that the internet infrastructure in the building was down, because my laptop still worked, but I had no /dev/eth0 device at all! I tried rmmodding and modprobing my network driver, e1000e, but no dice. I did two finds and a diff to determine that there was no change to all of /dev between the module being there and not. /var/log/messages revealed the module not complaining about any errors, though. In an act of desparation, I got the kernel module sources off the thumb drive I had originally installed them from, recompiled, and reinstalled. And it worked! I have no idea why.
No, apparently I am just having bizarre, reality-independent notions about network devices living in /dev.