The impact of the earthquake on 11 March in Japan on the Nikon Sendai plant will have significant consequences for the launches of the Nikon D4 and Nikon D800. They were to be launched before Summer to be manufacturer in Sendai. The manufacturing process will not be ready until the production is transferred to Malaysia.
Apparently, the Nikon D400 (planned for a much later date in 2011) is not impacted.
All in all, it may mean that everything is pushed to the last quarter of 2011. the exact launch order may not be currently determined inside Nikon marketing department.