Not sure if I'll take the n800 back for the N810.

On my N800, when in Notes, tapping the active entry field brings up the THUMB keyboard so the center button is not needed. However when in the web browser I must press the center button to get the THUMB keyboard to open.

The N800 screen will be okay in a car if you are able to move it to a shady part of the car which would potentially disconnect the GPS in a N810.