I am finding the D4 AF kills coming from a D300 / D700 - let us know if you feel likewise. I have this subjective impression that I just wave the D4 in the general direction of my subject and wham bam every photo is in perfect focus!
I sold my D300 this week. Bit of a fire-sale ($550) but with 72K actuations it was necessary to get below the low actuation models for sale locally to get any offers. I started the sale off asking $675 so I'm OK with that. Had to make some room in my bag for the D4 as I had too many cameras and the D300 wasn't going to get brought along.
With all these D600 rumors, I think I'll dump the D700 too. I don't like keeping equipment around for limited purpose especially if the market price might drop.
Anyhow the D4 is causing major disruption to my kit! This is particularly because I am finding it to be a very versatile camera, useful even in situations where I didn't expect it to be (birding).