Bernard, are you using the little 70-300 VR on your D3x? Is that lens actually sharp enough for the body? If it is, I'll run out and get one for mine (even if only as a stopgap until Nikon releases the lens we're all talking about here, and as a travel lens later on). I had noticed that lens recommended in this thread before, but I hadn't noticed that the poster was a fellow D3x shooter.
Nikon could release any one of the following lenses that would provide a reasonable FX telephoto option between the 70-300 and the exotics: I'd assume that any one would sell for between $1500 and $2500, weigh the same as or less than the 70-200 f2.8 AF-S VRII, and have AF-S, VRII, G and N designations, so I won't repeat the alphabet soup on each lens. I would hope that the new lens would be designed with the D3x in mind (as the 24-70, 14-24 and other recent Nikkors clearly are), so it would stand up to very high resolution full frame.
70-200 f2.8 really FX (replacing the present "DX" lens that is one of the best lenses made on DX bodies, but soft in the corners on FX)
70-200 f4 (smaller, lighter, cheaper and very sharp)
100-300 f4 (nobody but Sigma makes one right now, but theirs is very sharp, although not stabilized)
80-400 f4-5.6 (the slow aperture at the long end is a requirement of the laws of physics unless you want a lens the size of the 200-400, but it could certainly be made in an AF-S version, and sharpened up significantly with more modern optics)
300 f4 (I'd rather see any of the zooms, because they'd be more versatile, and a 300 f4 still leaves a hole between 135 or so and 300 unless an updated 70-200 was released at the same time)
Dave, I wouldn't switch, although the telephoto hole is really annoying - to get your D700's AF and build quality in a Canon, you're looking at a MUCH bigger and heavier body, and about $5000 (and much inferior ergonomics). Nikon WILL release the lens you (and everyone else) want - it's just a question of when. Canon has refused for many years to release any non 1-series body with high-end AF. Canon owned the DSLR market for many years, but seem to be resting on their laurels lately, and letting Nikon take more and more market segments.
Right now:
Ultra high resolution pro full frame:
D3x over 1Ds mk III - image quality, ergonomics, AF
High speed pro sports
D3 over 1D mk III - high ISO, AF, full frame instead of intermediate frame size that isn't FF, but won't take EF-S lenses either
Smaller full frame
Tossup between D700, 5D mk II and Alpha 900 - D700 has best AF, high ISO and ergonomics, Alpha 900 has best low ISO image quality and body image stabilization, 5D mk II has high MP in an established system and video.
High end crop frame
D300 over 50D - AF, build quality, ergonomics
Midrange crop frame -
D90 or D5000 over 40D (old) or high end Rebel - image quality, ergonomics, build quality (over Rebel, not over 40D)
Entry-level (D40, lower-end Rebels, lots of Sonys, Olympi, etc...)
Nikon is probably behind here, due to the D40's low resolution (especially if the D60 really is discontinued, rather than just out of stock).
As I see it, Nikon has the best body lineup out there, especially at the higher end (few D700 owners are looking at switching to a Rebel) right now, and we're probably closer to a 24 mp D700x than we are to a Canon with D700 level AF in a smaller body. I have more confidence in Nikon to release a great telephoto between the 70-300 and the 200-400 than I do in Canon to counter the 14-24, because the Nikkor is only a revision of an existing lens (unless they do a 100-300 f4, which is still a fairly simple design), while the Canon would be an entirely new lens and a massively tricky design.
-Dan