Here is my first submission for the arms portion of the challenge. I didn't know if I'll have time later on to do it so I just did it yesterday to post today.
A few notes:
I added FK/IK blend to the arms as required. However, I also added IK to the fingers with added functionality to interact either with something the hand is holding, or something outside of the skeleton like a surface, button, etc. I did this by adding IK to the fingers and parenting the locators that control their position to the IK hand controller. Then I point constrained those finger IK controllers to locators that are outside of the skeleton. If you place keys on the finger IK controllers, a blendpoint node appears, allowing you to blend easily between the location of each point. I added the lock_POS attribute to each of the fingers so that I could blend them all on and off of their point constraints. After playing around with it, I think I'll add some up vectors for each of the fingers as they are hard to pose otherwise.
I also used the pose deformers on the arm to keep the volumes correct. I used one on the elbow, two on the forearm, and two on the wrist. I may add two more on the wrist to correct some of the intermediary shapes, but it doesn't bother me too much right now. At least the wrist doesn't collapse onto itself. I'm finding out that for each body part, it is better to just add them to a new pose deformer instead of trying to work with an older one. They tend to conflict with each other easily if you don't do so. Also, I'm noticing that you generally need to turn the allow twist attribute off on the pose deformers as that generally conflicts with other poses on the same joint.
I used the screen capture software oRipa to get the videos. People on the forum were complaining that they couldn't see the deformations clearly enough so I orbited the camera around so you could see multiple angles focused on each deforming object. I also left the wireframe on for many of the views so you could see how the geometry is deforming exactly.
This isn't my final post for the arms challenge, so I welcome critiques and ideas. Let me know if you'd like me to make a tutorial on the IK fingers setup. I don't know how much time I'll have to do it, but it is very handy to have once your character starts handling objects.