Stumble up to your Mac first thing in the morning, tap the keyboard to wake it up and -- what? I incorrectly disconnected my Time Machine backup drive? I never touched it, I swear!
Turns out, this is not my fault for once. Apple has just released a support note explaining how, in a certain combination of circumstances, third-party USB hubs may incorrectly disconnect after wake from sleep, causing system instability. Basically, if you have a third-party USB hub that doesn't wake properly, is connected via another USB hub, and you wake your computer with an external USB mouse or keyboard, voilà, system instability.
So waking my MacBook Pro by tapping the Space bar on my Microsoft USB keyboard (wait... OK, I see the problem here) is enough, sometimes, to make my Time Machine drive choke.
The solution Apple offers: connect all USB input devices directly to a USB port on the computer, wake it by pressing the power button instead of waggling the mouse or tapping the USB keyboard connected via a third-party USB hub, and connect USB storage devices directly to a USB port on the computer to prevent third-party USB hubs from affecting them.
All I need now is for the next version of the MacBook Pro to have about 17 USB ports.