I always felt that DX was just a placeholder between 35mm film and the eventuality of FX sensors, and the time of FX sensors has come. I've been waiting for this camera because my brain never wrapped itself around the field of view/focal length connection with DX. I was always doing a 1.5 crop factor calculation in my head every time I shoot. Am I the only one who does this? I would shoot at 18mm and in my head I'd be thinking: "OK this is equivelent to 27mm focal length." Finally the time for doing such mental calculations is over. My 80-200 will cover 80-200 telephoto focal lengths again. It started at an awkward 120 field of view for many years and was fairly unusable for people shots. My new 24-70 will be a nice wide to short telephoto zoom. A 50mm lens will be a normal focal length again. My 85 1.8 won't require me to stand on the other side of the room to get a nice head and shoulders shot. No more crop conversions running through my head. I feel liberated.
Second reason - the D3 ISO perfromance in a smaller, lighter cheaper body. I don't need to lug a huge D3 to childrens birthday parties. I already get strange looks with my DSLR set-up among all the soccer mom's with their Canon digital elphs (but I get much better pictures But I can't wait to shoot available light and concerts at clean 1600 and 3200 ISO!
Now if they would just come out with some nice consumer FX zooms. Alas, I sold my 24-85 AF-S that I loved and they discontinued it, and the 24-120 gets widely panned. I new 24-120 AF-S VR would be nice sometime soon.