Hi,
As far as I know, the most efficient technique used in magazines (especially Playboy) for that "plastic look" is Photoshop...
There are several retouching filters that can be applied to erase grains, scars, etc from the model's skin. You barely can recognize the original model from the final printed pics.
Just as an illustration watch following link in order to see how "magic works" from the hands of one of the respected professionals in the art of photography and retouching for magazines like Playboy, Cosmopolitan, among others, Ms Marija Matijasec.
http://www.graphic-design.com/Photoshop/beauty_retouching/rollover.html#
See you,
Alx