Quote - Model the figure with the arms in the most common position, ie, down by the sides.  Make separate versions for raised and bent arms, then use geometry switching to bring them in when needed.

The same thought has crossed my mind at times. To play the Devil's advocate, I can see some arguments against it.

If you wanted to keep compatibility with character morphs, each new arm geometry would need to be a morphed version of the same geometry, with the same winding order and vertex count, and this would seem to negate some of the reasons for using geom switching. The geom switching would, in effect, be just a different way of applying morphs to the arms, but with the disadvantage that the change between geometries is a sudden discontinuity (not good for animations), where as a JCM can be applied smoothly as the arm bends. Also, if the arm is being rotated on two axes it can be affected by two JCMs, but you can't switch in two geometries at the same time.

As to Paloth's question "Can you set up joint controlled geometry switching in Poser?", yes it can be done. Switching is implemented via a 'geomChan' channel, and that channel can be slaved to a rotation channel in any of the usual ways, including using some intermediate channels to attain more control.  I'm less certain about the interaction between the rigging and the different geometries, but I suspect that it could cause big problems.

I don't want to pour too much cold water on the idea. Perhaps it does have something to offer in some cases.