After having a gripped D200 that was corrupting files due to a funky connection between the grip and the body I swore I'd never own/use a gripped body again.
One thing that no one seems to have mentioned in the D700 with grip vs. D3 discussion is that the D3 has two CompactFlash media slots.
That is a huge functional difference for a simple reason: it makes in camera "dupes" as easy as choosing that option; or if you don't wantt of that make the second card an over flow device or use it to put your NEFs on one CF card and your JPEGs on the other.
If I missed someone's prior mention of this, my apologies.