I've heard people mention concerns about skin friction before, and I really don't think it's an issue at the speeds we travel. It is an issue for the SR-71, but that plane isn't a very good example of an eco-friendly vehicle.
This isn't a very good picture - just a screen shot of of a youtube video, but if you watch the video, you can see that the air stays attached better on this wing made of fabric tubes, than on a comparably shaped conventional wing. Again, this wing is not designed to fly at anywhere close to the speed of sound, and neither are our cars.
By the time you separate all the forces that a car has to overcome to be put into motion and remain in motion - aerodynamics, rolling resistance, etc. - the drag coefficient of the difference of paint jobs, or plastic, or paper, is infinitesimally small.
This video shows that it is more about the aerodynamic shape than about the materials. Take a look at the Aerocivic. On close inspection, that car looks pretty rough. There are a lot of irregularities in the surface, despite all of the gap fillers and such. It doesn't look like something that the car manufacturers would put out as a concept car, until you stand back and look at the car from the bigger perspective, then it really does look like a concept car, and basjoos has put the miles in to prove his concept.