While everyone (it seems) is waitng for the new rig, with the facial expressions and visemes, I thought I would post this quick note to the Gallery about how to create visemes using the existing rigs in Blender. I am mostly using MH 1.1 (unstable) with Blender 2.70a, but for this instance I'm going to use MH Alpha 5.1 with Blender 2.63a (on a PowerMac G4 that someone gave me).
First is the drawing and conceptual page. As much as I love Preston Blair and Gary C. Martin visemes for the 'O' mouth shape, the problem is that they are focussed on 2d drawings, so an O looks like a elastic band. In reality, an 'O' shape is the combination of two 'C' shapes, mirrored horizontally:
It requires eight mouth bones to create this shape, which if I am viewing the video correctly is the number the new 1.1 rig uses:
And here it is, the most difficult viseme to create, using only pose bones, with no subsurface subdivisions. Better yet, you can add these bones to the muscle rig, without any major changes.