Hi guys.  The misss fast skin shader is actually a Mental Ray shader.  It's available in Maya, 3dsmax, and XSI because they all use Mental Ray as a rendering engine.

The quality that makes it unique to all other sss shaders I've seen in Carrara, Vue, etc.,  is that the Mental Ray fast skin shader uses multiple layers for the subsurface scattering effect, and multiple specular layers, which can all be controlled by maps.  It blends the multiple layers in a soft "overlay" effect, which makes hard shadows and bumps appear more diffused under each layer.  It acts kind of like real skin, which we know has multiple layers as well, and scatters light more deeply as you go down each layer.