Windows Down Or AC Up?

When I was toodling around the USofA in the 1970s it was in a climatological nightmare known as the VW bus. No air conditioning in the summer and virtually no heat in the winter, but at least I was paying only about 50 cents a gallon for gas.

So the question arises in this era of $4 gas: Is it better to drive with your car windows down in the summer heat or with the AC on? The answer, it seems, is some of each.