No, I haven't tried it, but it seems too complicated. I'd just use a motor with a disk attached to the shaft, and a lever from the disk to the jaw. One rotation of the disk will cause the jaw will move up and down once.
If you use a stepper motor, you can get the control you need (speed, and number of rotations) pretty easily.
ive never seen it done on a skull per se - but i have seen some larger animated monster faces done with it - i think thats the only way id ever animate a face - all these skulls are wonderful and great and are a tremendous showcase for your talent - but for a situation like my haunt - no one will really be able to pick up on the subtletees or realy be able to appreciate it unless they sit and get real close to it - i would however like to make a HUGE talking skull - that could get some attention - like 3 ft high or somethin - i dont think you could use the pneumatics for a realistic size skull, but i bet it'd be great for large ones - use some flow controlls here and there for the subtletees and you got a wicked piece! - riley