The comments in the "Carrying Style" post, below, came in about like I expected—a few pros shaking their heads over what amateurs consider "heavy" (photographers are beasts of burden, and some pros do schlep far more equipment than many readers might realize—see my favorite picture of a photographer here, and if you have any idea how to get in touch with the guy who took that—the mysterious and elusive "S Smith"—please—seriously—let me know)—and, of course, several people thoughtfully addressed the potentially serious health issues that can result.
Work-related injury is serious stuff. I remember a blacksmith I knew in Vermont who had such serious back problems that it could take him twenty minutes to stand upright again after shoeing a horse. He was a deeply traditional Newt (i.e., native Vermonter), but he practiced yoga every day—because it was good for his back.
Not all photographers develop physical problems as a result of carrying heavy equipment awkwardly for too many years, but many do. Personally, I developed a sensitivity in my neck that at one point seemed like it might be permanent, although it's gotten better in recent years. Before the UpStrap came along, I also had a distinct case of "shoulder hunch" that another commenter mentioned—the tendency to hold one shoulder higher in order to keep a camera strap from slipping off of it. As a result, I've become almost fanatical about lightweight equipment, and about carrying methods. That's not just preference—it's a health issue.
From this picture on the cover of my book Lenses and the Light-Tight Box (I can't find the picture file, and note that the book is no longer available), you can see my all-time favorite camera setup: An Olympus OM-4T with a Zuiko 40mm ƒ/2, and a Contax strap with a contoured shoulder pad. Note the spring clips on the strap: when I was concentrating on shooting, I'd unclip the strap and stick it under my belt so it was out of the way, and hold the camera in my hand. The large rings were for getting the strap back on quickly: I could just stick the whole spring clip through the ring and pull back on it. No fumbling.
Obviously this is a long way from a pro setup, but I "wore" the camera every day—put it on in the morning, and took it off at night, like my shirt (in imitation of David Vestal). So it had to be comfortable and light when it was on my shoulder.
I really liked those Contax straps—I bought five of them and still have a couple. Now, however, I'd choose the UpStrap RF, the UpStrap with the smaller shoulder pad. I can't say if the UpStrap is the best strap if you carry your camera around your neck—maybe an OpTech would be better in that case—but years of carrying too much equipment around my neck, as I say, has left me unable to carry cameras that way. I can't carry any camera around my neck for any length of time without pain. For carrying a camera slung from one shoulder, the UpStrap RF is far and away the best I've ever used—it stays up there admirably; you just don't have to worry about it.
I always thought that the best "camera strap" would be a simple setup similar to suspenders. They'd attach to your belt or pants in back and in front, just like suspenders, but they'd have extra straps sewn on each side at about shoulder level that held the camera. This would put the weight of the camera equally on both shoulders but keep it entirely off your neck. I've never tried it, though, so maybe it wouldn't work all that well—maybe the weight of the camera pulling up on your pants in the back would give you a permanent wedgie. I'm not the guy to make it into a product in any case (I just get ideas, I don't act on them).
As for carrying tons of equipment around, I'm just not that kind of photographer. It's not always a disadvantage. Some people carry lots of equipment so as to be ready for anything, and this helps them get certain pictures. But traveling light and staying unobtrusive can also help you get certain pictures, ones you might not be able to get if you advertised "photographer approaching" from a distance.
But back to the subject—newer and younger photographers would be well advised to consider this issue carefully. Carrying a heavy camera bag or several cameras draped around your neck might seem easy enough when you're young and strong, but burdening your body with awkward and uneven weights on a regular basis can do orthopedic damage over the long run. Beware.
Featured Comment by Janne: "The extreme fascination with 'pro' equipment among photography hobbyists sort of irks me. Not only does it propagate the idea that it's the equipment more than the users' skill that makes a good picture; it leads people to actually get worse equipment than they could have.
"My workplace has had some media attention the last couple of years, and we've had a steady stream of photographers and video people come by. One thing it has hit home is that professional photographers do not need better gear than amateurs, they need different gear. As far as I have seen, the equipment they use is made to last long enough so it can be deducted; it is easily serviceable or replaceable at a moments notice (no oddball choices); or it can be rented at a gear rental shops around the world. Size and weight, and purchase cost, just about never comes into it.
"We had one arts photographer come in to do a quick shoot. He was traveling light and brought only one camera, a Mamiya 7. For all that, he still had two or three bags full of stuff, including a strobe and power pack and a big, sturdy tripod that the camera never left. No problem for him because 'traveling light' still meant traveling with an assistant who could be counted on to pack and unpack, carry stuff, check reservations and so on.
"But we amateurs don't have assistants and we are often not primarily photographing so our gear really does need to be very small and light. And as 'small and light' usually means no tripod for us it means amateur gear needs to work well handheld, unlike pro gear which will normally live on a tripod. The extreme case is digital MF. There is no amateur market for it, not because of the cost (how much does a motorcycle, or RV, or golf club membership set you back?), but because it is so obviously unsuitable for amateur use. Digital backs assume you're shooting tethered and can use a dedicated computer with their own, expensive, software on it, so no stabilizer, no high-iso performance, lousy handholdability. But other pro gear is similarly unsuitable for amateurs, it's just not as blindingly obvious."
Featured Comment by Stevierose: "I have to say that I am in total agreement about being conscious of maintaining good camera carrying ergonomics (I mean, I have actually had cervical spine fusion surgery), but I think that, for me, the problem is more the camera than the strap. The problem, as I see it, is: so far there is no digital equivalent of an Olympus OM4t and 40mm lens pictured on Mike's book cover. This combination is: light, rugged, very well thought out (the highlight and shadow spot metering function is brilliant), has good optics, and (here is the kicker) it has a big, clear, beautiful viewfinder with interchangeable screens. I can carry an OM4t around all day on any kind of strap.
"I have purchased a number of DSLR cameras in the hopes that they were even sort of close to this kind of outfit, and, I'm telling you, they ain't out there. My latest foray in this direction was the Olympus e420/25mm prime outfit. But the viewfinder is a tiny little tunnel compared to the OM4t, it is nowhere near as intuitive a photo maker, and the lens is no great shakes. It is small and you can carry it all day. The new Panasonic G1 is being heralded as the inheritor of this tradition, but it has an EVF (albeit improved). Pentax makes excellent prime lenses and fairly intuitive camera bodies, but they are pretty heavy in my hands. So, I am still waiting. And, even though I am way into digital now, I can't bring myself to sell my old Olympus 4t."