OK, so I'm not the only one! I primarily use my iPhone with one hand and I often find that the phone suddenly handles like a stick of butter whenever I have to use my thumb to access something on the opposite corner of the display (i.e., when trying to reach the top right corner with my thumb while holding the phone in my left hand, and vice versa).

Space is a a premium when you design mobile applications, so I understand why buttons are placed near the corners. That said, I believe this particular design problem may be the result of not testing designs on an actual phone early enough in the design process. There are plenty of tools that will let you quickly test a design on an actual phone (Prototypes is one), but I think a good rule of thumb (get it?!) is: never place buttons for primary app functions in the top left or top right of your application. At least not unless you want to make your app significantly less mobile!