Here's a better graphic illustration (Green are positive magnets, red are negative, or vice versa):
[attachment=0]LIM-LSM.2.gif[/attachment]
With LIMs, the timing isn't as important, the copper fins on the car will try to catch up to the traveling wave (which you can see in the animation is moving slightly faster than the car). With LSMs, the switching of the electromagnets from positive to negative must be precisely timed as the magnet on the car passes over them.
Excellent graphic and explanation, but I'm still curious as to if anyone can explain why one time for me on S:EFK the train upon return to the station slowed down almost all the way and then rolled through the station and almost to the end of the track into that back area? My thought is maybe since its an LSM it might have not completely synced up on the returning brake run? Scared me a little but I figure its meant to happen. I just thought it was funny that the ride ops have to push the train back to the station by hand from there.