This video clearly shows how important mechanics are in executing squats. This girl smokes a much larger guy in an overhead squat competition. The guy's form is so bad though. IMO he was beaten even before they began.
http://www.crossfit.com/cf-video/CrossFit_OHSComp.wmv
http://www.crossfit.com/cf-video/CrossFit_OHSComp.wmv