Just finished implementing the moving buzzsaws. Hope you like the above image because it just took about two hours to upload it to my GameDev webspace - good job the Apprentice final was on.
The buzzsaws spin and move back and forth along an axis, defined in the editor. They can also be activated and deactivated by the same signals system that everything else uses.
I had some trouble getting the prismatic joint motors disabled properly - nothing I tried seemed to work reliably so in the end I had to stop them moving by creating two static circles, one on either side of the axis of travel. The spinning is not done by the physics engine since it seemed to make them unstable so is just a cosmetic effect so that was easy to get working right.
It's nice to finally have some other moving objects up and working though.