There are five ways to do mouse-like movement.
- direct absolute positioning: this is what a touch screen does: instant (x,y) position input. Great for tapping buttons, but no notion of relative movement (so not usable for e.g. an FPS game).
- physically implemented indirect absolute movement: this is what a traditional mouse does: it's a good and intuitive method (but no way you can integrate it into a handheld, you'll have to use an external usb mouse). You're controlling (dx, dy), not (x,y), but in doing so, you also move the device itself, so there's still a mental mapping between the absolute position of the mouse and the absolute position of the cursor, as long as you don't reach the edge of your 'mouse mat'.
- virtual indirect absolute movement: this is what a trackpad does: I don't like it as much as a traditional mouse because you're basically using your finger as a virtual mouse on a very small mouse mat. The advantage of modern real mouses is that they don't need a mouse mat so the area you can move in can be as large as you want. The mental position mapping suffers from such a small 'mouse mat'.
- reversed physically implemented indirect absolute movement: this is what a trackball does: basically it's an upside down mouse, where instead of having a moving mouse on a static surface, the mouse stays where it is and the surface moves (i.e. your thumb). This means that you have to mentally convert 2D movement speeds to ball spinning. To me, this is rather unintuitive.
- relative movement: this is what a joystick/nub does: you're controlling (dx, dy) absolutely, that is, holding the nub in a particular position means (dx, dy) is constant. This is quite intuitive and allows for a good mental mapping between mouse movement (not mouse position) and nub position.
I think it makes a lot of sense to have a touch screen and a nub, with the option to plug in other input devices. Touch screen and nub are nicely complementary because they're at two extremes of the spectrum.
