I've had a look at the sample photos Nikon put up on their website - per pixel sharpness isn't at all impressive but the amount of detail you get to work with is staggering, even on the "regular" D800. I'd probably go for the D800E, myself, even though I can imagine I'd run into moire a good bit it should be reasonably simple to just downsample and wipe it out.
Their sole ISO 640 image (from the D800) has a fair amount of noise visible in the shadow area, don't know if ETTR would help that (although the "original data size" suggests to me that it could've been bumped up in exposure a good amount) but it's a pleasing type of noise distribution, and I didn't see any noise in the subject areas. Good detail on small patterns too.
Not a bad release so far, looks like! Hope the 5D3 can catch up, but we keep hearing it'll be a "low mp" release.