Actually, safety nets aren't exactly 'safe'. You have to be *really* careful about landing on them with proper weight distribution - otherwise you can easily break your ankle, leg, wrist, tailbone, ect. One of the first things they warn you about is landing in an L position that will make your knees smash up into your face. I think I read someone about someone breaking their neck on one in Sam Keen's book "Learning to Fly".