It's funny, I think that maybe I'd rather see a 12 Mp A900 than a 24 Mp D700 ...
Did you ever consider the A900 + autofocus Zeiss lenses, or what made you choose the D700 ?
Was it the Nikon glass you already own, or the low-light performance of the larger pixel pitch (lower pixel amount), or ... ?
Switching to A900 would have cost me about... well, it wouldn't be enough to sell my car. Lenses, flashes, accessories. Even selling my Nikon glass, the second hand value would be less than half the price for new Zeiss glass. considering the state of the economy it also makes sense to minimize new investment at this time.
Zeiss glass might be sharp, but I really like the focus to rear-out-of-focus transition rendering of the 85/1.4D. And the 135 DC is unique to Nikon.
I like the nikon flash system.
Low-light performance is for me - at this time - much more interesting than megapixels. The reason is simple - for my high-resolution landscape work I use film, 6x9 cm, 6x17 cm, 4x5", 4x10", 8x10". 12 Mpx goes a long way for the intended use of the D700.
Also, Sony is new on to SLRs. They seem to have gotten things approximately right, but that's not enough for me to dump my Nikon gear already. Time will tell if quality holds up.
I will likely consider Sony/Zeiss again 2-3 years from now.