First of all, Sony didn't necessarily STEAL the motion technology from Nintendo. Nintendo didn't really come up with it either, there were some original PS1 controllers that had it, and I'm sure there were some even before that. Besides, the motion is even different because the PS3 can not tell how far away from the system the controller is ... so it's not really the same technology.
Secondly, if I am going to play a game... I'm not doing it to get in shape or get off the couch. I want to relax and go ON the couch. Honestly, if I am going to stand there swinging with my controller, I might as well not play the game and do it for real.
But in spite of all that, I will get one because the whole presentation intruiges me and I think it will be a pretty good system.