Here's another tip on mirror lockup - if you are shooting landscapes & macro on a tripod, then I've found it best to use Live view to frame. Because it has to move the mirror out of the way to show you live view, it is the same as mirror lockup. On the 5DII you could not autofocus in live view without pressing another focus button. With the 5D3, you can zoom 10X to the spot you want to focus on, press the shutter release half way down, and it will focus on that specific spot, giving you a green box overlay when it has achieved focus.
With the new view screen, it's really sweet because of the resolution, even at 10x. You can verify with your eye whether or not it's in true focus. I've found it to be very accurate.
The major point - when you use live view, it's the same as mirror lockup. It's how I shoot all landscapes & macros. With the 5DII it was manual focus at 10x. with my new 5DIII, it will be auto focus at 10x.