For me the 4 inch screen is the perfect size and I think that apple will stuck with It for some time. 
I can not image what will happen with the Samsung Note II, rumors have it going to 6.3" or 6.5" that is just crazy
I was really hoping for a 3.2 inch screen, that is the real sweet spot. In fact on second thought you can do anything with 3 inches you can with 3.2.
it should be small enough to sit in your palm and you can text but people cant really see the phone, a "palm phone" excuse the pun, not from "palm" but in your palm, 2.8 inches, oh ok maybe even 2.5 inch 320 X 460 screen wow, that would be heaven.
Wife iphone 5 is like a big tv remote ! Lol if you need something that big use a iPad! I stick with oringinal style than the wannabe tablet 5 size
One handed use is a necessity now a days.
Here are some prime examples, when responding to a text while driving its very hard to use both hands so thats one case,
You're joking right?
Nope.
I wish they would go back to the 3.5 inch screen and dump the 4 inch. Anyone else wish for the smaller screen?
I liked the 3.5" screen better than the 4". Maybe I just have small hands, but I have trouble using the iPhone 5 one handed.