[assaflavie]

I actually find the scroll motion to be very easy to perform using my index finger. However, I do agree there are issues to consider when it comes to usability. You definitely want to prevent unintended gestures and clicks/taps. So for one thing, the back touch doesn't necessarily have to be "on" all the time. It may be a mode that you enter under certain circumstances. And perhaps more advanced gesturing algorithms are needed to filter out intended from undintended gestures - maybe giving more weight to the size of the touch area, so that you palm resting on the back doesn't register as an event.

I don't pretend to have the answers to all these issues, but something tells me that smartphones can do much better than the current state of the art when it comes to game controls, to pointing at precise location, etc. And it goes without saying that this won't work with the existing mobile OSs as-is.