It depends what you do. I personally would want to be in a group if I were in a dark alley on a Sunday night, but I have no reservations walking down the streets of Brisbane, Sydney, or Vienna while I was over there with my camera.
I would actually be more worried with a smaller camera, since many pick pocketers would prefer to avoid confrontation. A small camera is something that can be grabbed on a dash past, and something the pickpocket may even be able to use. Large cameras are rather different.
Use some common sense though. If you have say a Nikon D200 which unfortunately says Nikon D200 on the strap, tuck it under your collar so people from behind don't see it. Always have your camera strap secured around your arm or neck, unless you have a tripod or something else to make the camera even bigger and more difficult to snatch.
As for plane trips I always take my camera in hand luggage. I have never had an airline complain about bringing a camera bag in addition to a normal backpack on a plane.
