I've propped airplanes since I was 12 and it is as dangerous as you want to make it. I've propped everything from Cubs/Luscombes/Culvers (Cadets) to Stearman's and a Stinson Jr. S and a variety of Cessna nosedraggers. I've also done the hand-cranked inertia starters (a truly kick-ass way to ignite an airplane). I say this only to give a glimpse that I've done this before. So, saying that I will say this: The first time I propped an airplane for real I was alert, paranoid, and uncomfortable to a healthy degree. And this was with my Grandfather (30,000+ hours, etc) in the cockpit holding the brakes, controlling the switch, etc - in short, the person I trusted most in the world. After propping many airplanes I will say that the last airplane I propped I felt the following: alert, paranoid, and uncomfortable to a healthy degree. I guess my first rule is - if you've never propped an airplane, learn how from a person that's done it before you attempt it - I don't believe it should be a self-taught type thing. Second - never trust anybody in the airplane. If you call for switch off and brakes - assume the switch is hot prior to touching the prop and give yourself an out. Press the hub of the prop to see if the brakes are really set. Do not just trust that because you asked for it, the switch is cold and brakes set. Third - every prop is hot - never assume that it isn't (Also, when hand-towing a nosedragger pushing the prop-hub assuming that you will maybe somehow stumble, stroke down on the compression stroke and be chopped into a million pieces. Those are just some rules of thumb that may be helpful. And - never get "peer-pressured" into propping an airplane if you feel uncomfortable with it or haven't done it. If the guy insists, tell him you'll sit in the cockpit and he can prop it.