I wrote the autorig script in MEL to rig this face. While this version of the script does a decent job of rigging a face fairly quick, it does not have the ability right now to add extra joints for better control on the face. I will be addressing this in the next version of the tool.
Also, this rig does not have any corrective blendshapes. For better deformation, the user will have to make corrective blendshapes as needed and plug it in.
This entire rig is built using constraints in Maya. So, it is very light and portable to all versions of maya that have Parent, Point, Orient and Aim constraints in it.
You can find more info about the rig on my blog: