Slashdot has a discussion about mice with a scrollpad (images here), which functions as a vertical/horizontal ‘scrollwheel’. Meaning that besides scrolling up and down, it also allows the user to scroll left and right. Uh. It’s like a touchpad, the ones you regularly find on laptops.
I think that’s the worst invention one can think of: integrating a ‘touchpad’ on a mouse. Every laptop I tried (and used) I ignored those things.
Here’s a far better idea for simulating that scrolling movement: put a small stick on it. Remember the IBM laptops with their red ‘pointer sticks’? It probably works better as a third button too. Plus gives you the additional advantage of having two mice on one mouse. Tired of moving the mouse, just switch back to the pointer stick mouse.