I had $7K put away for the rumored 24MP D3x that I thought would be announced in 2nd quarter 2008 and hasn't yet. I must say that the D700 completely suprised me. I'm too busy right now to used the cameras and lenses I have already, but I'm going to get a D700 within 3 months to have a small, light D3. I decided that I'd use it more than a 24MP camera. It's a matter of useful resolution and getting the most GOOD pictures.
The problem with a 24MP camera is that MOST people will never take advantage of it and would be better off maybe with a high MP medium format. My logic is as follows.
First, you MUST use any 24MP on a VERY good tripod and head or be in a studio with almost blinding flash. Your certainly not going to get more detail than with a D3's 12MP. Motion blur will wipe out the detail in the extra MP's and all you are doing is increasing your processing time. If you want more detail, ALWAYS shoot from a good tripod with anything over about 6MP and probably even there. I try to always shoot from a tripod with shutter delay on now when it is at all practical. It's just not always practical.
Second, you are going to have to stop down to F8 to F14 or you will not see the extra resolution because of lens limitations with even the best 35mm glass, under most conditions. .
If your predominately a studio photographer or a landscape photographer then maybe 24MP make sense. But even the landscape photographer could just take two rows of 3 pictures each with the D3 and stitch it together for even better resolution.
Right now the camera that will give me the most resolution in many shooting situation is NOT the D3, but the D300 because it allows me to put more megapixel on the subject I want with a given lens because of the DX crop factor. But, most of the time, when I'm NOT pushing the limits of a telephoto lens, the best sharpness or resolution is the D3 because the large photosites let me bump up the ISO without significant noise when I'm handholding or there is a moving subject
More MP usually DOESN'T mean more detail, unless you can meet all the other conditions that it requires. MOST of the time what limits the resolution of your photo is how many kilo of gear you can carry.
D3, D300, D2X & D200 New 14-24 F2.8 too! If your not shooting Nikon your doing it WRONG!