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I figured I would chime in on this
Arguments about things warming up are mitigated to some degree by the fact the car was allowed to cool down while they added the dimples.
Cruise control was used on both runs.
The mythbusters results of a 11% difference Would tend to rule out most variations between the 2 runs. (not to mention the fact that the clean and the undimpled clay car got almost exactly the same mileage)
Also of note is the fact that the windows received no dimples. this would mean that air flow over the windows would be almost like it was stock. the dimples over the top of the car would have ecited the boundary layer air over the top of the car thus getting more of the air flowing over the top of the car to flow down the rear window. This combined with the relatively stock flow over the windows would have reduced the C pillar vortex strength and thus reduced induced drag.
As far as suggestions that the dimples up front would only contribute to drag this isn't entirely true. The dimples up front would keep the boundary layer thinner all along the car and enhanced the performance of the dimples towards the rear of the car. It is not totally uncommon to use two or more rows of vortex generators to get this effect. I'm currently trying this out in my simulations and it is quite effective.
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