Charles,
Mirror Lock Up (MLU) really comes into play on long exposures, and/or extreme telephoto shots where any vibration will be noticed. Wildlife photographers use this extensively as many of their shots are at long telephoto ranges and generally less than ideal conditions.
In landscape photography (i.e. storm photography) camera vibration is not near as critical. The wider angle is used more as you're trying to get as much of the storm as you can, If you're using extreme telephoto, your subject is most likely moving (tornado demolishing a building) and you're fighting wind and excitement.
I have used MLU in lightning photography. I haven't seen where it makes a big difference in whether the shot is good or great. Where I've seen the differences is in Macrophotography (really close up stuff). Any camera shake shows up here, so the MLU makes sense to get the sharpest photo possible. I really doubt that you will be trying to get an extreme close up of a flower or bug with a tornado bearing down on you. If you are, then you deserve what you get!
The effects of camera motion can really be seen in several of the videos that have been posted. Especially those where the shooter was two miles away and trying to zoom in on the tornado trashing a building or crossing a road. Any time the photorapher tried to pan, the movements were magnified due to the extreme zoom level. This is where MLU would help in still photography. It give a chance for the mirror to bouce up and the vibration from that to die off before opening the shutter and exposing the shot. Now you see why MLU isn't really good for Storm Photography. There is a certainl about of time involved and too many things happen in that time frame for it to be feasible.
I would be more concerned with higher shutter speeds to stop the action and eliminate the camera shake. IS (Image Stabilized) Lens help in this regard allowing you to use a lower shutter speed in less than ideal lighting situations.
Higher ISO settings are another solution, but come with a price tag of higher noise (film grain to all of us older film folks).
Now that I've written more than most people ever wanted to know... I hope it helps.
John
