I appreciate what Mark posted.
I think much of what is being described as maai in this thread is inaccurate and over simplified.
Maai has a space and time element to it, and there is not one maai.
Maai is definitely one of the most critical factors and one of the most difficult principles to master in the martial arts.
Watch this video with I Liq Chuan instructor, Daria Sergeeva. She does an excellent job of demonstrating the importance of learning to not broadcast any body movement before striking. And you can see when she does broadcast, that even completely untrained people can naturally sense her movement, and respond accordingly.
I wanted to address this even though I feel it should be in another thread, because it really isn't directly related to maai.
Frankly, I was not impressed with this video. What is being shown is very important and yet I do not consider it a high level skill.
Here is a video that I came across a few years ago that features a much better demonstration of the same thing (from an unlikely source in an impromptu situation!).