i find to really test a skin shader you have to test a lot more than very ambient lighting situations.  i've used PR2 in low light situations, but i think i did some adjusting to do it.  it's hard to say, because i haven't tried the same character in the same scene that way, so i keep changing texture and target skin tone, too.    also, there's a tutorial here on using fastscatter with a control map to get certain places to do backlighting SSS right.  i think i'm going to try to incorporate that into my adjustment of PR2 soon.  i've had pretty negative dealings with fastscatter in the past, but maybe it's not so bad if you limit it to just a few places (ears, nose, edge of the fingers, a touch on the lips, etc.). 

personally, i presently add veins in postwork because it's very important for me to control their visibility, orientation, length, and thickness based on where they are on the figure and (for artistic reasons) the lighting.  i mention it because it would probably be better with a control map.  i probably wouldn't handle veins procedurally myself, because i find i need to change veins when i paint them.  i would probably want more control than a node can give.

but, as i think you mentioned you want to, i eventually would like to be able to paint photoreal skins, as seems to be suggested and done by the experts at CG society.  perhaps with various shader-controlled layers (freckles and sunspots, veins, burned in AO, etc.).  i know from my PR2 experiments that i'll want to make good SSS maps.  i don't know when i'll ever get to that, because right now i'm experimenting  with modeling and UV mapping Blender (think a toddler with blocks) and wishing i knew python.  but i figure Antonia will give me the opportunity to try my hand at a lot of new 3d development tasks.