I was watching one of the commercials and noticed they demonstrated the many touch features of the iphone. I saw the zoom feature where you had to use 2 fingers making a gesture to zoom in on a picture/etc. I have never used or tested an iphone but it seems as though the touch feature would be a pain in the ass having to deal with such a small screen and gestures such as the one mentioned, maybe i'm wrong
From my experience, it is very simple to use. It'll definately be harder to use it one handed but with two hands on the device, it is very easy to zoom. The screen surface is smooth and easy to glide your fingers across too. I guess you have to just give it a try. You'll never know if you never try.