According to Quesabesde the Nikon D700 replacement is postponed till October 2011 and the Nikon D4 is expected to be announced in early 2012. This delay was caused by the earthquake in Japan.
In the past few weeks I have been receiving conflicting reports on a potential delay for the D800 and I am not convinced that this is the case. I still believe there will be a major Nikon announcement in late August. The Nikon mirrorless solution is probably delayed based on previous statements from Nikon representatives indicating a potential March/April announcement.