Gofaster -- Yeah, the rules are different for digital cameras that aren't dSLRs. SLRs are big and noticeable, and everyone can see you had one. Had our colleague been looking down the lens of the camera, this problem wouldn't exist -- everyone would have known he was taking photographs.
But, the fun of a digital point and shoot camera is that little screen. They will claim you shouldn't use it to compose for stability reasons, but I do anyway (parallax screws me up all the time). And if you've got a camera with a tilt lens (I use a nikon e995), you can take pictures from all kinds of angles. Plus, that screen means it has all kinds of menus, including the option to TURN THE NOISE OFF. Most cameras have an AF confirmation light. Learn to use that -- it's unambiguous and much more discrete than a beep. And if you're using an SLR, turn off AF. It'll only eat batteries, make noise, and mess up photographs
Besides, I'm betting Borg here can move his wrist quicker than the AF can acquire and lock.
And, yes, digital cameras do have a shutter, and their operation is audible. These days the way they take pictures is pretty much the same (well, except for the fact that non-dSLRs are basically glorified "point-and-shoot" cameras, so you don't get a decent optical viewfinder, and you don't get quite the range on the F-stops (Mine tops out between 9 and 14, depending on the zoom). And the graininess (noise) of ISO settings above 100 is noticeable (dSLRs tend to be 200). I mean, you can set the sensitivity higher, but it reduces the overall image quality.
And you don't announce you're taking pictures, you mumble it (I'm going to go take some pictures). They hear something about photographs, and when they figure out what you're doing, they're not bothered by it. Hell I pack a minipod and set that thing up inside, and most people don't even notice I've got a camera.
