Upload & Sell: On
I've dipped a toe in the Nikon arena with a D1X, D7000, and Fuji S5, but it is very hard to keep both systems going. Personally, I hate the Nikon owner's manual and menu system, finding it counter-intuitive and poor terminology -- having a much longer history in Canon gear.
The D800 is very interesting, and maybe it's good I haven't sold all my Nikon lenses yet! But otherwise, I'd say the smart thing is to sit tight and see if a replacement for the 5D is in the wings with better focusing. Even used, the D3 is far to expensive for my taste, and I'd prefer a D3s to the old 10MP original, but it's even more expensive.