Skin is fascinating, this is not a skin tones tutorial but more of a skin optics kinda thing. Btw I never went to art school or whatever, so erm, this is not the absolute word on the topic, just a collection of thoughts.
For info about what brushes I use check out the Blending Tutorial:[link]
I'm using Photoshop CS2 and Wacom Intuos 2 for this.
Edit: apologies to those of you who are freaked out by the little skin balls, hahahahaha, sorry really