I fly a GoPro HD on an RC plane and it produces superb video.
There is a great scooter home movie of scooting in Saigon, it appears to be made with a GoPro. I lost the link to this but am looking for it.
Sometimes I plug the Gopros video out (not the HD video out) into a transmitter on the plane and send the tv image down to a receiver on the ground. Fat Shark goggles are plugged into this receiver and I fly the plane while seeing the image through the GoPro that is mounted on the plane. The tv out image is not HD but it is very flyable anyway. The GoPro is recording the HD image during these flights. This kind of flying is called 'first person video', as if you are in the plane. For more info look at the FPV forum on RCGroups.com.