On a regular snowboard, the sidecut is one smooth line, which give the traditional look of a snowboard.
Have you ever noticed that a serrated knife cuts through bread much easier than a regular knife? That is because it has multiple points to focus the pressure, making it easier to cut.
The same concept is use on Lib Tech/GNU snowboards, so that you have an easier time keeping your edge on hard and packed snow.
The picture above shows an exaggerated example of how magne-traction looks. Imagine when you are riding on ice or hard packed snow, you put your regular board on its edge, and you will have two main points of contact digging in, giving you grip.
When you ride a magne-traction board, the same thing happens, only you have multiple points, which give you a much stronger edge hold.
Generally magnetraction is used on rocker boards (which normally have a weaker edge hold than camber boards) which gives them the advantage of a loose riding feel, but edges when you need them.
Confused yet? Have a look at some of the magne-traction boards available.