If you need to get your hands on a Nikno D800 when they are released, you can pre-order now at various online stores. Supply from Nikon will be limited based on pre-order sales. Amazon already sold out or pre-orders and notes:
Note on Availability: This item is in high demand and supplies from the manufacturer are limited. Its availability will fluctuate, and if the item is not currently in stock, we cannot guarantee that we will receive additional quantities in a timely manner. We will not charge your credit card until we ship the product.
A review of Nikon's D800 can be viewed at UltraPortableTech D800 Review
Nikon D800 will be released in March and the D800E will be available in April.