No offense but you have to be a complete and total idiot to not buy a screen protector for your iPhone, iPod Touch and iPad.
I've had my first gen iPhone for over 2 years. I've thrown it into walls, lost it onto concrete, dropped it on asphalt, lost it from a moving car onto asphalt, kept it in my pocket with metal keys etc etc. Just from walking in the streets I've probably lost it over 10 times alone, face down in the asphalt (either slipped from my pocket or my slippery hands!)
Seriously, I treated it like ****. The aluminium back has some bulks, fading color and a lot of scratches, but the screen never got any scratches. Not a single one.
I know Ive been lucky, but it really seems the iPhone glass will break into pieces before it gets scratches. FWIW, I've seen much more iPhones with crushed screens than scratches. So from my experience these thin extra films doesnt make much sense. Some kind of protection on the back does, however - although if buying an iPad I know I would miss that direct contact with the cold, delicious aluminium