D4 (and D800) available seems to me to be totally random.
I didn't even decide to go for a either of these until mid-March. I put my name only one "big" vendor; I was told I was #44 on the non-NPS list for the D4.
I happened to mention to two of my local camera stores that I was interested in both cameras when I was in for other things. I had zero expectation that either would get enough units to make it feasible for me to get one from them.
I was, therefore, highly surprised to be called last Wednesday by one store that a D4 had come in and was mine for the taking (well, buying), so I went right over and grabbed it. The next day, the other store called that a D800 was in, so I claimed it and picked it up on Saturday. Totally random. I have no idea why I got lucky.
I hope all those still waiting get their D4's and D800's soon. Being an instant gratification kind of guy, once I decided to buy, I couldn't wait. (Actually, the D800 is claimed by my wife, so I don't know that I will get to use it all that much, but the D4 will be in my hands.)