The D800 is a triumph as people here know. It's price/performance is astounding and it'll be loved by the many people who'll buy one.
That said there seems to be confusion one the place of the D4. As someone who've able to buy both I've been thinking about them relative to each other and will share why I'm still buying a D4.
1. Build. The D4 is a tougher camera. Even the card-bay-doors are metal. That makes a difference to a few people. To that few, it's vital.
2. Speed. The big one. The D4 is faster. If you need the speed the D800 is no substitute.
3. Resolution. The D4's files are smaller but large enough for 99.9% of uses (including fashion, landscape and portrait work which are all being done today, on DSLRS with fewer pixels). The world kept turing when the Ds MkII was resolution champ. Magazines didn't shrink. Billboards weren't all shot on MF backs. If you're shooting away from home, being able to transfer files faster (more than twice as fast) matters. Extra pixels are literally a waste of time.
4. Precision. Given enough resolution for almost any scenario, the benefit of the 36MP sensor is cropping. This is most useful if you don't have lenses with the framing you need, or you're not able to capture the who you need in the moment. Professional D4 users have all the glass they need and are skilled in getting the framing right.
This isn't to suggest the D800 isn't awesome. If it was faster I'd have one. That said the D4 is Nikon's flagship and meant for a very specific market. Professional shooters working for publication.
I think the extreme excitement is because the forums are dominated by landscape shooters and amateurs. Landscape shooters ability to use tripods, wait for light and use long exposures means they have the ability to compensate for things which make the D800 impossible, or impractical, for those that don't. Amateurs don't have the glass, the money, or the skill to exploit the full potential of lower-resolution cameras because their photos are made in the edit and need to be cropped.
Unless you're printing a crop, or at a a giant size AND that giant print will be viewed close-up - which is incredibly rare - the D800's file are bigger than you'll need.
What they do offer is the ability to reduce size, and reduce noise, without eating detail. This is how the files will be used in the real world most of the time. Appearing in print, or online, at normal sizes with NR applied when used at higher ISO.
For those shooters they'll have a cheaper, smaller, less robust camera with a much smaller shot-per-charge capacity. Their images will look almost as good as the D4's after noise reduction at higher ISO, and better at low ISO if used very, very large - which will e almost never.
That's a reasonable set of compromises and the one Nikon are selling. The D800 doesn't make the D4 redundant. It slots in below it, exactly as it's supposed to. It'll be very hard to find an outlet in which the D800's resolution is visible (unless you're cropping or shooting at low ISO in controlled conditions).
With the D4 you're buying a lot of advantages that professionals crave, and losing some of the 'cushion' that amateurs rely on and features some professionals (product photographers, MF guys and landscape shooters etc., don't need.)
The D4 is the best 35mm camera Nikon have ever made. The D800 is a good 35mm and an amazing small MF body, which predictably lacks the speed and strength of a best 35mm bodies.
It's a great time to be a photographer. The future looks exciting.
That said there seems to be confusion one the place of the D4. As someone who've able to buy both I've been thinking about them relative to each other and will share why I'm still buying a D4.
1. Build. The D4 is a tougher camera. Even the card-bay-doors are metal. That makes a difference to a few people. To that few, it's vital.
2. Speed. The big one. The D4 is faster. If you need the speed the D800 is no substitute.
3. Resolution. The D4's files are smaller but large enough for 99.9% of uses (including fashion, landscape and portrait work which are all being done today, on DSLRS with fewer pixels). The world kept turing when the Ds MkII was resolution champ. Magazines didn't shrink. Billboards weren't all shot on MF backs. If you're shooting away from home, being able to transfer files faster (more than twice as fast) matters. Extra pixels are literally a waste of time.
4. Precision. Given enough resolution for almost any scenario, the benefit of the 36MP sensor is cropping. This is most useful if you don't have lenses with the framing you need, or you're not able to capture the who you need in the moment. Professional D4 users have all the glass they need and are skilled in getting the framing right.
This isn't to suggest the D800 isn't awesome. If it was faster I'd have one. That said the D4 is Nikon's flagship and meant for a very specific market. Professional shooters working for publication.
I think the extreme excitement is because the forums are dominated by landscape shooters and amateurs. Landscape shooters ability to use tripods, wait for light and use long exposures means they have the ability to compensate for things which make the D800 impossible, or impractical, for those that don't. Amateurs don't have the glass, the money, or the skill to exploit the full potential of lower-resolution cameras because their photos are made in the edit and need to be cropped.
Unless you're printing a crop, or at a a giant size AND that giant print will be viewed close-up - which is incredibly rare - the D800's file are bigger than you'll need.
What they do offer is the ability to reduce size, and reduce noise, without eating detail. This is how the files will be used in the real world most of the time. Appearing in print, or online, at normal sizes with NR applied when used at higher ISO.
For those shooters they'll have a cheaper, smaller, less robust camera with a much smaller shot-per-charge capacity. Their images will look almost as good as the D4's after noise reduction at higher ISO, and better at low ISO if used very, very large - which will e almost never.
That's a reasonable set of compromises and the one Nikon are selling. The D800 doesn't make the D4 redundant. It slots in below it, exactly as it's supposed to. It'll be very hard to find an outlet in which the D800's resolution is visible (unless you're cropping or shooting at low ISO in controlled conditions).
With the D4 you're buying a lot of advantages that professionals crave, and losing some of the 'cushion' that amateurs rely on and features some professionals (product photographers, MF guys and landscape shooters etc., don't need.)
The D4 is the best 35mm camera Nikon have ever made. The D800 is a good 35mm and an amazing small MF body, which predictably lacks the speed and strength of a best 35mm bodies.
It's a great time to be a photographer. The future looks exciting.
My d700 upgrade =D4 FTW!!! 
i ordered in the first 30 min tbe preorder became available.
