I've heard that some newer DSLRs have a "Quiet" mode that reduces the noise the camera makes when you take a picture (as mentioned in answers to some questions) How does it work? Are there any potential consequences from using this mode, like a reduced shutter life?
Quiet mode slows down the motion of the mirror when it goes up and delays it going back down until the shutter-release is released.
Normally the mirror going up and down is the loudest noise the camera makes. So slowing it down causes a longer shutter-lag but makes less noise. Also, the mirror normally comes back down immediately after a shot is taken so that you can follow action and compose the next shot. In Quiet mode, the mirror stays up and your viewfinder remains black until you release the shutter at a time when noise is less disruptive.
Shutter life is not affected at all since nothing changes for the shutter. The mirror actuation mechanism should last a little longer but no data to that effect is provided by manufacturers.
An additional note on noise reduction (of the audible kind), if you really want to eliminate it use either a blimp or a range finder camera.