[Joeri]

The ipad disproves your claim about gestures. Gestures work just fine, as long as you do them on the screen itself and make them tightly correspond to real-world behavior. The usability problem occurs when the display and the touch interface are decoupled. The intuitive aspect of direct manipulation hinges on the manipulation actually being direct.

The trouble with mice is that they are a double proxy. You move the mouse in absolute terms, the mouse moves relative to a surface, and that relative movement is translated to the screen. The mind after a while abstracts away the mouse into a piece of your hand, so touchpads aren't really an improvement over mice, because you're just making relative movements on a proxied surface in both cases. In my experience the big usability issue with touchpads vs mice is that the area for relative movement is too small, requiring frequent repositioning. Apple gets it right by making the touchpad surface huge, so that you reposition your fingers less.

I expect that the current form factor is just an in-between until most computing devices look like ipads with external keyboards, with the mouse reserved for precision work (or perhaps we'll have dual finger/pen touchscreens).