So far, my experience with the motion detection system is that it does work, but it's simply not fast enough. The CHDK version was able to get some cameras at under 50 milliseconds from detection to getting the image. On my 60D have only gotten it down to 240 milliseconds or so (locked manual focus, live view silent shooting mode 1 or 2). That might be long enough for a really long chain of lightening flashes, but from scouring the Internet, most lightening chains are less then 200ms long. You can never catch the original flash - that's what triggers the exposure. However, most lightening fires several flashes along the same path, and those secondary flashes are what you can hope to catch.
The best suggestion I can offer is this:
-Set up the tripod
-Use the widest lens you have. Add an ND2-4 filter or a circular polarizer
-Stop it down as far as you can without while maintaining sharpness
-From a safe place (it is a lightening storm after all), point your camera towards the storm, focus it and set the focus to manual. Frame your picture for best effect
-Set manual exposure. Between the filters, ISO, F-stop and the lighting situation, you are looking for an exposure that is at least several seconds long. The more lightening the storm throws, the shorter the exposure you want to keep the picture from being saturated.
-Turn on the ML intervalometer and set it to fire continuously. The idea here is that you want the shutter open most of the time, so that if lightening strikes in frame, you will capture it.
-Sit back, and enjoy the storm. Periodically stop the intervalometer and repoint the camera at the best part of the storm.
-If you see lightening that should be in frame, note the time: it will help finding the right frames later.
The ML silent-shutter mode that captures images straight from the live-view buffer may get a better response time. I think most of the lag is in the detection mode and the camera - from shutter closed, the 60d is supposed to be able to fire a picture within less than 100ms of pressing the button, but from live view, it just doesn't appear to be able to go as quickly. The ML silent shutter mode might be just what you need.
If nothing else, you could make a nifty timelapse of the storm.
Alternately, if you don't need the high-res for prints, using a high-def video mode is probably the easiest way to capture single bolts.
Here in Tucson during one of many monsoon storms I attempted to use the motion detector in ML to photograph lightning. It seemed to work when the T3i detected a change in the light level, that is the camera took a picture. This is my first attempt at photographing lightning and as everyone knows you will never know when it will flash but with ML on the camera it would seem easier to catch the flash. Can anyone offer more tips on lightning photography?