It's been hard to find enough time to get finished, but, here's where the arm rig stands at the moment. I've got it able to bend backward in IK and have a soft IK that I adapted from one made by Andy Nicholas for another program...there's one difference that I made that would allow for the bicep and forearm to be scaled differently and I'm sure the constraints used and the way they are combined would be different. I'm going to add the resizing next, then I'll see about putting it in Squetchy Sam and running a bunch of tests.
Here are a couple of quick clips showing the arm and some of what it does.
elbow_with_soft_IK_03_22_2010.mov
elbow_no_soft_IK_03_22_2010.mov
arm_test_03_22_2010.mov