No way would Nikon want to wait another whole year to launch the D400. The D300 came out 3 years ago. Nikon seems to be on a 3.5 year schedule for these bodies, so best guess is first half of 2011 for teh D400. The D4 is another story...mid to late 2011 is more like it.
An undeniable paradox: To think that there is any such thing as an absolute rule is at worst naïve, and at best, shortsighted. There is no such thing as an always-true, all context- or situation-salient, absolute rule that always holds true…including this one!