To get a SSS effect on a diffuse material you need to connect a node to the transmission pin (you can see this on page 99 in the manual).
A simple setup to simulate skin is a mix of a diffuse material, which will give the diffuse reflection and some SSS effect, and a rough glossy material, which will give some glossy highlights.
The glossy material should be quite rough (like 0.1 or so) and can have specular set to 1.0.
Connect an RGB node to the transmission pin of the diffuse material. Set the diffuse value to a skin color, and the node at the
transmission pin to a brighter version of this color. If you have a texture apply it to the diffuse input.
The medium node can be set to a scattering medium. The absorption should be set to blue or cyan, so it
lets mainly red light pass through. Adjust the scale slider until you have the right amount of absorption.
Connect both the glossy and diffuse material to the mix material. Adjust the amount slider to get the right amount of glossy reflection.
If you also have a bump map with your skin texture, apply it to the diffuse and glossy materials.
edit by abreukers
re: "Using Medium Nodes" used to be on page 99, new edition manuals may have this on another page. For the online manual, Please see "Using Medium Nodes" on http://render.otoy.com/manuals/Standalone/?page_id=368