Still using my original iPhone 2G 16GB. The screen is in perfect condition - no marks, scratches, nothing. The top corner has a gouge from a particularly nasty fall, but other than that it's in excellent condition. I'm as happy with it now as the day I bought it. Still does everything I need to and very well - haven't found a reason to upgrade yet.
I repect what you are doing, but have you used an iPhone 4?