Apple 30" Monitor Intermitently Flashes Off and On
I don't know why, but if you unplug the monitor power (not just press the power off switch) and then plug it back in the problem goes away.

My guess is that the on/off switch on the side of the monitor is heat sensitive and calibrated for the temperature of the room, if the room temperature changes, things become un-calibrated, and the monitor starts thinking it's receiving a touch even when it's not. 
The stan marsh method resets this calibration.