My older son (9 yr) has started to use the power drill - no drill bits allowed for now, only drive bits, he uses it with drywall screws to assemble small plywood parts for his projects.
So far, no accidents. Today, together with his little brother and an older boy from the neighborhood, they made a cart from a plank of wood and 4 training wheels - leftovers from their old bicycles. It actually worked although it's probably not the most solid construction in the world.
Am I a bad parent if I allow him to continue using the power drill? I did my best to teach him how to use it, but 9 years seems pretty young.