First, it shows up in Nikon Official Website. Then, it was taken down. Of course, this is the Internet Era, someone has already capture the screen image of the rumoured Nikon D3X. It may have a sensor of 24.4 MegaPixels. So far, there are no other news. Don’t bother to head down to Nikon USA. The information had been removed.
One screenshot of D3X in the official website