1. I can use this one handed, that button over in the opposite corner doesn't look too far away. Reach for it. 2. My palm hits a button in the bottom-nearby corner. 3. Undo last action. 4. Try for the button again. 5. My palm hits another button the bottom-nearby corner. 6. Undo last action. 7. Oh right, that home-button trick. Double-tap the home button. 8. Reach the button.
I don't try to forget that functionality, but it doesn't occur often enough that I instantly think of it. In fact, having used iPhones since the 3gs, the go-to-move when you needed to reach a button out of reach with one-hand way the nose-press, which still comes more naturally to me than "reachability."
I guess if you can train yourself on it, it's good, but after having to use my wife's 4s the other weekend, I long to return to those days, size-wise.