Zagg = overrated.
They won't do squat if a drop causes a cracked screen.
I've had 3 iPhones, 2g, 3g, 3GS never used a case on any of them. The current 3GS has been dropped a few times and zero damage. If it hit just right, screen protector or not it will shatter, simple as that. As far as scratches, BS. I've run my keys across the face of my 3G and 3GS, never a mark. It's marketing to get to you blow 30 bucks on a pc of plastic film.
My wife actually wanted a case when taking over the 3G and the back is in worse shape now since the case traps dust and small particles that rubs around between the case and the phone. The black back looks worse after being in a case for a year than it did the prior year unprotected. All the screen protectors imo are a joke and a suckers bet.