Okay, I love the screen on the side, but here's how it could be better: Instead of a touch scrollwheel, make the wheel a physical thing round the outside of the device. To scroll, spin it with your thumb, or run it down your arm, or your coat, or the wall of the underground train. To see the screen and scroll at the same time, you'd run it along the table infront of you, pick up, and run along some more. For extra points, the wheel should be slightly loose to let you flick and leave it to spin. That'd be good, to pull the environment - and using your body as a surface - into the interaction with the device.