I believe your shoulders should be back. However there should be no piching sensation. If you stand straight and relaxed your arms will hang at your side. If you bend at the waist and begin to assume your golf posture and relax your shoulders, your shoulders will "round". Now if you keep your shoulders relaxed and round and stand back up you will notice that your arms and hands are no longer at your side but in front of your body. This causes seperation of the arms from the body on the takeaway. This is the exact opposite of what Ben Hogan taught in his book. My theroy is when you stand straight and relaxed and begin to take your golf posture, keep your arms at your side then grip the club. You will take the club back with your shoulders, and not your amrs. Also your shoulders will stay on a much better plane and make it easier to turn. Just my opinion