I haven't seen any official numbers, but just to give you some idea, my udoo draws about 2.4W at idle when nothing is plugged into it other than power and a 100M Ethernet connection, and with the SAM3X Arduino CPU in its default do-nothing state (though it does get slightly warm-- putting that CPU into low-power sleep if it's not being used could perhaps save a fraction of a watt). This is with the Wifi module removed, though-- from memory, that pulls about one additional watt, even when not being used. During a kernel compile (make -j5 uImage) I'll see occasional peaks hitting 5W. That's in pure text mode-- using the onboard GPU for any serious graphics or video playback will probably add to this, but I haven't done much yet on the GUI side. Of course any attached USB devices, SATA drive, etc. will draw additional power. As a theoertical upper limit, the four RT8287A switchmode regulators on board are each capable of delivering 4 amps, at 5V, 3.3V, 1.5V (for DDR3 RAM) and 1.2V (for i.MX6 CPU/GPU core). Maxing out all of these rails simultaneously, total power output would come to 44W, perhaps 48W at the input (4A @ 12V) after taking regulator losses into account, but of course that's highly unlikely to ever happen.
