Digital Home Thoughts: The 'Super-Secret Spy Lens' for DSLRs

"Remember that very first time you went out with your shiny new SLR, determined to shoot some Pulitzer-worthy people shots? You know, real stuff. Candid shots of people just living their lives and doing real things completely unaware that they were on camera. It's hard. People have a sixth sense for knowing when someone's taking their photo. Especially so when you've got an SLR and a big lens pointed right at 'em. Our Super-Secret Spy Lens is the answer."

I'm not entirely sure on the ethics of something like this - taking photos of people without their permission - but I have to admire the cleverness of it. I've heard of devices like this before, but haven't purchased one. I'm somewhat tempted to buy one, because I really like candid photography, but suffer from SPS (Shy Photographer Syndrome) and can count the number of times I've asked strangers if I could take their picture (here's one example). I also wonder what it does to the quality of the image captured. Anyone used something like this before?