How much does a camera vibrate due to your finger pressing the shutter or the mirror flipping? Camera Technica decided to conduct a test by strapping a laser pointer to the hot shoe of a Canon 7D. They then filmed the red dot on a far wall against some text while shooting normally (i.e. pressing the shutter with a finger), using a remote shutter release, and finally with a remote shutter as well as mirror-lockup.
You might be surprised at how much movement the camera experiences even if the shutter is pressed carefully. Lesson learned: for the sharpest possible photos, use a tripod, a remote shutter release, and the mirror-lockup feature on your camera.