The site was down between 2:20 and 2:55 AM PST. A fairly important network switch at our datacenter was plugged into a power strip which somehow got turned off. Our best guess is that a rat stepped on the toggle.
The site is back up, and that switch is now plugged in to a more appropriate source of power. (In other words, not a power strip.) Infinite props to sherm for driving out there and getting things fixed so quickly.