If you've got a case with a decent sized lip around the screen, why do you need one? It helps with less surface area being exposed in your pocket and lessens the likelihood of contact on a bad drop. I only had one scratch on my screen, and it was the iPhone 3G. You could barely see it when the screen was on. Since then, I've had every iPhone and never had a problem. I've worked everywhere from IT, to construction, to now CNC machines/machine shops.