I am certain many of you know that head by now, and Jorge Jiminez seems to have concluded his skin research resulting in this:
On his blog you find more about it, there’s a precompiled techdemo running in DX10 as well as the full sourcecode available.
There might be some intresting algorithms in there for… well anyone developing anything with CG 
I think the believability has a lot to do with the context and composition.
It’s easy to say a bald head without any noticable secene you know is artifical looks not so realistic 
If you know it’s artificial it’ll never look realistic to a cg artist, you’ll most likely always find something giving it away.
If you have no composition going on you know it’s artificial.
And if you rip it out of any context and make a humanoid head on mars you’ll smell theres something fishy 
But I agree, it doesn’t look too realistic, I think it’s because he neglected the oil-layer on the skin. His skin looks too dry, almost like cold wax covered with powerder.
While in another shot it looks like it’s made of plastic, too specular…
But I guess that’s tweakable and the artists duty.
Nonetheless he seems to have written a very potent algorithm for realtime SSS. I cheer for both the artistic and technical side of the project, and if you compare an individual (or in this case 2 people) against nvidia R&D, he gets the baloon and star-sticker from me