I helped a friend with a small-product photoshoot two weekends ago, and was struck by how quiet,and short, the shutter release sound of the new Canon 7D was. We had a lady, one of the business partners, who needed a portrait done, and she was a habitual blinker. The 7D's quiet shutter was an advantage, I thought. The sound of the mirror rising and the shutter were almost "as one". The mirror return was also very quiet...it was an amazingly quiet shutter system. Habitual blinkers often blink based on sound or on watching the camera, I am convinced, so the quieter and faster, the better. With very slow, old,mechanical cameras like 2 and a quarter rollfilm SLR's, the mirror moves up slowly, and loudly, and the lag times are pretty long. Same with some of the older long-roll studio cameras, where the electric lens diaphragm systems are loud and slow and telegraph the shutter release to people who tend to blink habitually.
