Can someone tell me what exactly this function does? I know there's also a switch right below the lens mount. I've read the manual for my hd100 but still unclear. thanks.

Nevermind, I should learn to read more carefully. :) Anyways, do people use this function? And any opinion on it's effectiveness?

The idea is pretty good, but in what I´ve shot so far I haven´t been getting good results from the areas of skin detection (you need pretty consistent, uniform lighting for it to detect all the relevant skin areas). For now I keep it turned off, I have yet to find a shot with too much skin detail.

I'm familiar with this from my last JVC (GY-DV500), and it's a neat feature - I only used it for specific situations, but even with SD it did a good job. I didn't have a problem with detection. Using the "range" setting, coupled with the feedback using the zebra switch produced good settings, although sometimes I would need to choose a different area to resample the base color. It does take a little time to do properly, but it does definitely "heal" some skin problems, and soften age lines. Of course it's generally women who appreciate the effort!