That is a good observation, I am interested in the new Viliv X70 Atom due out in April
http://www.myviliv.com/ces/main_x70atom.html

Here is a video of it being held and I can't make my mind up if it just slightly cumbersome
http://www.myviliv.com/popup/x70cf_bae_popup.html

The 4.3" of the N800 is a tad on the small side and perhaps 5" is the best compromise?

So far I have not seen any announcements of MID's with 6" screens though.