The concealed d-pad and button were among my reasons for buying a cut-rate N800 rather than waiting for the N810.
If, as Promethh says, the N810's d-pad is worse than the N800's, well, that's bad.
I haven't used a 770, but it looks a lot more usable. I had assumed that Nokia had heard enough about it that they'd put a good one on the N810, even if it was in the wrong place.
Seems to me they'd have been better off to keep the N800 size, and d-pad, and shift the qwerty to the left. Then they could put an array of buttons on the right of the slider, and have decent game controls with the slider out. (All games for such a beast would ignore the d-pad center button, allowing proper rocking of the d-pad.)
Oh, well, just makes me glad about not getting the N810. If the N900 is even a further step down, I shall doubtless purchase an N810 -- when they hit the $240 point.

As for the N810's size, I doubt that would bother me much. But it looks like the kick-stand is substantially shorter -- that would hurt. I hold the N800 in my left hand, with the kick-stand fully deployed and my fingers under it. My thumb is on the left edge, mostly, but I can slide my hand to the left and reach up over for the d-pad and buttons. I was about to recommend this grip to alleviate light-sensor troubles, but I fear you would need very small fingers to hold the N810 like this.