yea that true that aircon sucks power,
but one would imagine that the drag factor created by all the air pouring into the car with the windows open would make it less efficient than with the aircon on
and of course this would change from car to car
a small car with the aircon on full blast will drain alot of power and fuel, but on a big car, like the suv's that they where useiong (ford explorer xlt's i think - if i remember rightly) you would think that it would be more efficient for the aircon to be on, than the wiondows open
but hey, it is interesting
PS:
is anybody willing to do some test with there skylines - it would be interseting to see what the diff is (by tests i mean like 5 litres of petrol and see how far u go sort of thing at a constant speed)