For some reason, once in a while BookFour disappears. It doesn't even show up in Disk Utility. Usually turning it off and back on will bring it back. It didn't today. I unplugged it from the chain, plugged it back in. No good. I plugged it into a USB port. It worked. Remove it from USB, put it back on firewire, nothing. Reboot, it's all happy.
It's weird, and it's annoying. It's not a huge problem, 'cause that drive doesn't have any critical unattended purpose (unlike, say, the time machine drive and BookThree).
But this, combined with the occasional need to forcibly power-down the machine and reboot it, is making me rather irritated.
And if I complained to Apple, I guarantee you they'll blame the non-apple-supplied RAM.