According to a comment left on a Photography Bay post:
I quized a Nikon rep today he confirmed the D800 is coming but the release date won’t be till Feb March 2010
Obviously we have no way to validate. If correct, that puts the D700 at around 20 months old when it is replaced, which is on the short end for Nikon DSLR's, but possible. However, we'd expect a D700s to be more likely (D700 with video and hopefully the ISO improvements from the D3s) - typically going to a new number implies a new sensor, and we don't really expect a brand new sensor from Nikon until the D4/D400. Source: Photography Bay on 11/17/2009. | 
