I have cut some of the pink insulation foam(just like the blue stuff) in to a simple delta wing shape for a R/C model. The stuff cuts like butter with a 2 flute carbide bit, I was cutting at 40 ipm. I have nevercut the white foam but have carved it before and that stuff isnt as strong and makes a HUGE mess. As for the fiber galss on the foam it works great and when cured is hard as rock. I do use a vacuum bag for doing glass work tho, that allows you use less resin(less weight) and gives a nic finnish. I have even seen a Hovercraft prop made out of foam and fiberglass for the main thrust prop that was more than strong enough for that application. As far as getting the foam out of the blade, in model airplanes its really more work(alot more) than any weightloss you will get. The thin section of foam just doest really weigh that much.
Darren