To continue the discussion about camera size....
In an earlier post the other day, reader Edwin Liu commented that how you carry the D3 has an impact on how comfortable you'll be with it:
"Oh, on the shoot to carry ratio—just one hint: do not carry the D3 round your neck!! Yes, it's like a chainsaw if you do. The camera was designed to be carried in your hand(s), not round your neck. I usually carry the D3 as a walk-around camera in my hands and I never feel it. Trust me, it is so well designed for your hands that it feels like part of yourself. When you are not shooting, carry the camera in a backpack, not in a shoulder bag."
I think Edwin's on to something here: how you carry a camera has a lot to do with your perception of the size and weight it should be. The D3 with a large zoom is at an uncomfortable transition point—just about too big for a neckstrap. It really does demand another kind of carrying strategy, like Edwin says. It's true that relatively more weight is more comfortable in a backpack, and I know from experience that carrying a camera in the hand all the time is in some ways more comfortable than having it dangling from a strap digging into your neck: I carried a heavy medium-format camera around D.C. for six months and never even owned a strap for it; it was always in one hand. Never bothered me. Of course it does tend to limit what else you can carry, and what else you do with your hands. But it's a good way to make a relatively heavy camera tolerable.
There's probably a "break" or transition point between that method of carrying and carrying with straps. My habit is to carry a camera on a strap hung from one shoulder, which militates for a certain size camera as being most comfortable and handy (and a certain size of lens, too—big lenses make cameras the wrong shape for carrying the camera from one shoulder, unless the lens is long enough to make the whole shebang hang downwards).
But there's another "break" in size relative to carrying style: it's when you go from carrying a camera on a strap, to putting the camera in your pocket. That's why there's relatively a lot of discussion surrounding the size of cameras like the Canon G10, and the Canonet I pictured here yesterday: they're certainly small when hung on a neckstrap, but they're large for a pocket (I suspect the same will prove true of the Panasonic G1). So they're sort of at yet another uncomfortable transition point. A truly pocketable camera needs to be smaller still.
Same thing goes for really big cameras, come to think of it. Various famous large-format photographers transport 8x10 cameras on big tripods by using...an assistant! So, basically, they've got Sherpas. (Reminds me of one of my favorite Richard Avedon quotes—paraphrasing—"I don't need a motor drive; I've got a motorized assistant.") I think it's safe to say that if you carry your camera via Sherpa, you don't need to worry about its weight—an 8x10 on an extended tripod becomes perfectly portable.