- You hide parts of the content you are reading with your finger
- You might accidentally click a link (in the browser)
- Scrolling through long texts means you have to sweep with your finger from the bottom of your screen to the top, several times
Apart from scrolling, this could act as a nice volume control in media players. Maybe even make the scroll wheel pressable, so we have another button (mute in media players?).
If you have an N800, please try this the next time you want to scroll a webpage: Move your finger over the top right side of your N800, between the "Nokia N800" text and the speaker holes. I don' t know if the scroll wheel would fit onto a smaller device like the N810 (or the "N900").
I think a touchscreen is nice, but having hardware buttons makes the device just easier to use in my opinion. I would even try to make touchscreen clicks by pressing the display, like it is done with the new Apple MacBook touchpads (see apple.com for videos). But there may be patent problems with that, so maybe this is the reason why we won't see that on the "N900". But think about it! Wouldn't it be nice?
That said, please also improve the D-Pad and hardware keyboard on the new hardware :)