(UPDATE: The systems are getting back online.)
It happened around 4:10PM on January 17, 2012.
The systems that are working at Fukushima I:
Cooling systems for Reactors 1, 2 and 3
SARRY (cesium absorption system by Toshiba)
What's not working at Fukushima I:
Spent fuel pool cooling systems for Reactors 2, 3, 6
Gas management system for Reactor 2
Nitrogen injection system (since restarted)
TEPCO's switching station in Minami Iwaki had a problem that caused the voltage to drop momentarily. They turned the switch off for a few milliseconds to clear the system.
TEPCO doesn't know what caused the problem at the switching station.
The systems are getting back online. Kurion is still stopped. None of the systems needs to be continuously operated.
(There is absolutely no urgency in either question or answer, so I think everything is dandy now. I'm signing off.)