Completely change the Android UI and its elements like adding new battery meters, enabling wireless-n, enabling better camera features, changing the Radio version to improve battery, reception, camera, install software from other devices that normally you wouldn't be able to do, system image backup including apps+ app data at will, pair bluetooth devices such as wiimotes and controllers to play games with, turn the phone into an ftp server, no need for a parent software installed on PC to manage the phone (iTunes), CHROME2PHONE (or the much better Firefox2Phone) - something iPhone does not have, and so on and so on.