Well, not to turn this into a Mythbusters thread, but I don't always put my trust in what they find. Entertaining? most definitely. Case in point, they did a show on fuel economy, A/C vs open windows, using a Ford Bronco. I can't remember whether they said "nodifference" or "A/C uses more gas", but my van gets 2 to 3 more MPG with A/C. I chalk it up to a difference in aerodynamics of different vehicles.