I never used any screen protector of any kind with my 3GS. I was also careful never to put anything in my pocket with my iPhone. The front screen is absolutely flawless with no scratches. I would think it is safe to assume the same will be with the iPhone 4S but I heard rumors that the back glass is weaker. Is that true? As long as the back is as strong as the front, I don't think I have to worry though.