Not sure how long it would take to implement it, but it would make a lot of games more enjoyable, or even playable
The idea is that most games require a resolution of 320x200 or 640x480. The N900 screen is 800x480, so there are 160 pixels unused.
Well, what if the unused pixels are used as a touchpad, in order to move the mouse pointer? Two virtual buttons (left and right) can also be added.