In the 320mA case (I dont have the datasheet on the LEDs, so I assume 20ma) didnt really happen until I converted the cube to using shift registers (originally it just used 20 pins, and 4 resistors, an it only lit one LED at a time.). With the shift registers, it changed it so that it was lighting 16 LEDs at a time, and it needed 16 resistors instead of 4. I should probably stick some transistors on the plane pins, and replace the shift registers with ones that will support 160mA.
I have a couple other cubes that are running a fair amount of electricity (kill-a-watt shows about 1/2 watt). They run off of USB wall warts one is 500mA, the other is 850mA, and my guess is that they are using all of it. Those cubes use 16 lines, and im pretty sure that they are lighting no more than 8 LEDs at a time. One cube uses resistors, the other cube does not.
If i run a cube off battery, I should be able to measure the current.