In today's two 15 minute sessions I show how I used the smooth paint blendshape weights tool together with flood and a lattice to make an mouth open blendshape. This workflow was much faster for me than what I was using before (smooth binding to joints then painting weights there). I guess this may not be as useful if not using blendshape for mouth open.
During this process i also noticed i need to make a modeling change as the lips appear to be too wide in default pose (its nice to make these sort of finds quickly before any other shapes were created)
Hope you find it helpful.
paint blendshape weight hot key would be helpful to smooth a region, or flood a region. and a mirror blendweights tool would be helpful too.
Dan Bailey's online tutorial (http://userpages.umbc.edu/~bailey/Courses/Tutorials/ModelNurbsHead/BlendShape.html)