I know it's almost cliche, but for some reason it is a very effective hook. I think it was getting to use a real hammer instead of his little plastic one.
What he really enjoyed was when I showed him how to use the claw to take some finish nails out of the board. Once he figured out how to do that, he was taking them out and putting them back in again over and over.
This gave me a chance to build a four-foot French frame for my second prototype. this frame includes two 1x3's for the sides (poplar) and two of the cleats were ripped from 1x3's.
But the most fun was working with the GIT.