Steve coming up from the d300, the D4 absolutely kills, its shocking. I also think that in the last few years we have come to a time that digital everything has reached a mature state of being. I think we are in a very lucky time, that whatever comes next be the D4X or D4S, it may not be better, just different. I have found this to be true with audio at my studio, (my bread and butter is audio recording). Digital has gotten so good results with new digital products are not better, they are just different.
I have to say, I grew up as a kid with my grandfather in his darkroom. I had my own for years in my parents basement and as an adult. When I bought a digital camera (D200), I went with it. I honestly can say I don't really miss the whole film process. The one thing that I never got over with digital was the cropped DX format. Picking up the D4 with the FX sensor is huge for me, I'm sure I'm not alone in saying this but I now realize that I never really got used to DX format. Not to say I wasn't getting great shots, I just finally feel like I'm home.
At the end of the day the D4 does everything better than my previous body, I am very impressed. The only way this rig will take a bad photo is because of user error.