Of course 35mm was a bit of an accident too, I seem to vaguely recall. But to me it's the sensible size for an SLR all things considered, including depth of field.
The great thing about DX is that it is just about pocketable, and some of the Sony and Fuji offerings are mouth watering.
Back to the D600 - I traded the kit and got clipped a bit - but I couldn't face the agonies of selling online here.
First impressions - performance is utterly superb, enough resolution to see how bad you are and clean images at ISO 6400. The depth of colour is astonishing.
The size and weight are terrific, and the construction is fine. With a 35mm or 50mm lens on board you can carry it around all day.
I am already starting to enjoy the interface, though I think I'd prefer the four banks of the D300 set-up if pushed. The dreaded green auto mode, and the rather useful flash off auto mode, are very useful if sharing the camera, and i have set it up for portraits on U1 and sports on U2. I'll keep it on a general setting for using P, S, A and M. Of course the whole thing has moved on since the D300 and the modern improvements are terrific, video included.
The biggest issues/ trade downs from the D800 relate to focussing and the checking thereof. The use of the centre button to check the focus point I do miss.
Mind you this would have been far less useful anyhow as there are fewer focus points and the area they cover is a little small, especially coming from a D300. Of course this second point would still be a bit of an concern on the D800, as it is partly a DX/FX issue.
It will be interesting to see what this means if shooting my 85mm wide open with a subject to one side of the frame, as is often the case. Will the need to lock focus and recompose affect the very thin DOF? let's see...
it would have been interesting to see what might have happened had I had a D800 to hold, though maybe it's as well as the less one sinks in a body the easier it is to justify the next one when it comes along, though frankly it's becoming hard to see what one could want beyond a D600....