This is the first civilized dimple discussion I have seen in a long time. I usually run for the pitchforks and torches.
Here is Aerohead's response to Mythbusters. From what I have read here, dimples are weak vortex generators, but VGs only work in one direction, and VGs are called "band-aids for bad aero." If you properly shape a car, VGs, and especially golf ball dimples, would not help, and someone pointed out in the thread I linked that they put dimples all over the car, while it only had a chance of helping where there would be detached flow, like the rear window.
There have been many discussions on golfball dimples on here, with people explaining the Reynolds Number states dimples will not help on an object larger than a golfball, round, and spinning.