>The mirror lockup >is for sensor cleaning and maintenance, and reducing vibration >on slow shutter speeds/long focal lengths.
This is only half true. You cannot use Mup for sensor cleaning as it doesn't open the shutter. You have to use a menu item for that instead.
In the Liveview handheld mode, your first push of the shutter release raises the mirror and opens the shutter to allow the image to show on the LCD. When you press the shutter release halfway, the mirror is lowered to allow the camera to autofocus and set the exposure. Then when you press the release all the way down, the mirror flips up and the camera opens the shutter to make the exposure. So handheld isn't a "mirror up" kind of thing.
The "tripod" mode is a bit different. You press the shutter to raise the mirror and allow the screen to act as viewfinder as before. In this mode, you press the AF-On button to focus (or press the remote button for over a second), and the mirror stays up while you do it. This allows you to get the focus right while you're looking at the LCD, which is darn useful. Pressing the shutter _still_ lowers and raises the mirror before taking the shot, and it does so between each shot if you're shooting in continuous mode. So tripod mode doesn't seem to be a "mirror up" kind of thing, either. (Although you can set Custom Setting d9 to delay shutter activation for a second after the mirror goes up).