Use of Imagenomic's Portraiture plug-in for Photoshop to smooth skin. I find this tool to work well and is very easy to apply. For best results I use the eyedropper tool to select a representative skin tone when I bring up the filter and it auto-generates a mask so the smoothing is only applied to the skin. I usually just apply the default without tweaking the parameters and then I sometimes fade the filtered layer. I rarely have to do any masking beyond the automask the filter generates itself.