An alternate view on "trading up"
I feel the same way. I currently have a D90.
I have been keeping an eye on the D600/800 situation, but feel that neither are a true replacement for the D700 I sold a while back. I enjoyed getting back to the "full frame" look but felt the D700 was too loud and often attracted unwanted attention. I'm hoping that Nikon will release a D700 upgrade at some point in the not too distant future or else I suspect I'll be using my D90 for a while yet.
In defence of the D90, when I take the time to PRINT (10x8, 8x6) images made with both it and the D700, I'm hard pressed to spot the differences (depth of field considerations aside). Probably not what Pixel Peepers want to hear, but...