My Nikon collection includes the F, F2, F3, EL, FE, FM2n, FA, F100, D5100, and D700 [just sold to help pay for my newest baby, the Df].
This conversation is interesting to me because my reaction to the Df is that Nikon wanted a non-professional prestige/nostalgia camera Just Lke the M9. I became more convinced of this when I learned that the camera was first thought up and initially designed in late 2009. It does for the NikonHead (tm) exactly what an M9 did for the LeicaMensch (tm), ie, provides a full frame enthusiast worthy digital camera to the user of the traditional / original camera that made the company's fame, with as many of the same interfaces as could be managed while having it be digital. It goes for much the same market -- while $2700 looks very pricey to current Nikon DSLR users who know you can get a D800 for basically that amount and a D610 for $900 less, it's an affordable premium price for the nostalgist with bucks who is the Nikon equivalent of the LeicaMensch.
Size: it's smaller than the D700 and F100 (which were practically the same size). It's about a quarter inch thicker than the F3 but the same as the F3 in all other dimensions. It's lighter than the F3. It has the High Eyepoint type prism housing of the F3 which contributes to making it look bigger than it is, somewhat as when a man wears a substantial hat.
To a D700 user the Df feels small and light -- a little too light, some have said, though I quickly got used to it. It does not feel as if it was intended for, or could hold up to, serious professional use. But it's a full frame camera that takes the pre-Ai Nikon F lenses, some of which, as the 85/1.8, have a very special look. I cannot quite find the words to tell you what a pleasure this camera has been to use, how right it feels in my (small) hands, what a pleasure it has been to have a full frame digital camera with which I feel as I'm still in charge of taking the picture.
Is it in fact Nikon's M9? Basically, yes, with a much better sensor at half the price. I wouldn't turn down an M240 however.... which is not as large as the M9, correct? And whose sensor is rated (DXOMark) very close to the Df's.