Here is my time-lapsed video of the process I go through when painting a portrait in Photoshop CS3 with my WACOM tablet, using mainly the airbrush and some customized texture brushes.
Also a nice demonstration of David Nagel's Photoshop Skin texture brushes which I cherish so dearly! They're fantastic for blending tones together while keeping the texture of the skin intact and looking real.
These are the Skin Texture brushes I use when I'm painting portraits to capture that epic realism! This is just an example of how awesome and simple they can be, and how much of a difference they can make!