All comments apply to the N800 only...

I find it difficult to control the d-pad and center-click separately; the d-pad should be higher than the button, not lower, and it doesn't work all that much better holding down the center button and rocking the whole thing, even when the center is not used. (It gives me a sore thumb, too, after an hour or so of Tyrian...)

I actually think we'd do quite well with one of those little nublets they use on some digital cameras. I searched around on google images for 20 minutes, but can't find the sort I'm thinking of, and don't know what sort of camera it was, but way pleasing feel; with a bit of modification to support 8-way (and "rolling it" from one direction to another, just like an old C128 stick I remember...), it could be a great fit; even in the limited space on an N810-like design. (It stood out as a marked contrast to the nubs on a SE k810 and Rio Karma; the former was a pain, imho, and the latter was nice as a jog input, but not suitable for gaming. The more so since it was on a camera, where it was used only for jogging, and where such UI elements (not used while snapping pictures) are often bad.)

The zoom/fullscreen buttons on the N800 are OK, but a little small and continuous-feeling for gaming. (They don't bother me for much else...) Placement is right there, though!