Samsung's SCh-V960 may have the first optical joystick available on a phone, but we'll be damned if we can figure out what the hell that means. But we can take a look at Samsung's "fingerprint recognition" joystick patent to get a better idea of how it's going to work.
The fingerprint algorithm can detect where you place your finger on the joypad, which finger you place, and even the angle you place it at. That means sliding around with your thumb could get you your contacts, whereas using your other thumb could scroll through menus. And the placement of your finger, of course, knows in which direction you want to scroll.
Just conjecture for now, but it seems a likely candidate for the optical joystick implementation. What's also cool is that it can gauge how healthy you are by the amount of boogers you smear on its sensor.