You know, there was a time when I wondered by people like Britwrench post so infrequently anymore...

After all this, I finally realized that I didn't phrase the original question properly. What I was really asking, is: "I wonder what it would be like to drive a car via changing the demand for manifold vacuum/pressure, rather than the throttle opening?" The only way to achieve this WOULD be via DBW. I'm wondering if this was ever attempted before. If any of the big players attempted it, I'm sure they haven't released the results. Maybe there would be NO difference. If you have ever driven a car that has a vacuum gauge, you can see that it does (fairly) closely follow the movement of the accelerator pedal. I understand what nize is saying though. I need to get my head out of the clouds (or get an airplane). A vehicle designed to be operated on surface roads has completely different requirements than one that is designed to be above the surface. Probably the most important one would be having the ability to make instantaneous changes, as the possibility of unexpected changes in the direction/speed of nearby vehicles (multiplied by the # of vehicles on the surface roads) is many orders of magnitude greater than it is above the surface.

After giving it some more thought, maybe it would be clearer, if I stated it THIS way: If the CAUSE is opening the throttle, the EFFECT is manifold vacuum going down (or absolute pressure going up). My idea was basically, to turn that on it's head, completely reversing it into: The cause of wanting to raise pressure in the manifold, would have the effect of opening the throttle. But I suppose that sounds like non-sense to most people. Maybe I should just say, case closed. I know what happened to the cat.