Mid-Sole Cleats

I recently started reading Joel Friel's blog, and he had several posts about mid-sole cleats. 

He kept emphasizing how much benefit came out of these. That there was a greater power increase due to the lower center of gravity.  One of the statements he made to back up the lesser use of calf muscles was the analagy of doing squats.  The difference is doing them on the balls of your feet versus pushing the weight toward the back of your heels. 

I can understand these points, and simply based on this there would seemingly be very little reason to not switch to mid-sole cleats.  However I would like to know someone who has had experience with these type of cleats.  From my experience a slight movement in the position of a cleat can result in a knee problem for several months.  I would assume that the benefits given by having the cleat moved backward would be vastly overpowered by any knee problems that could result. 

The other problem that I can see resulting would be from the greater use of some muscles and the lesser usage of others.  If an athlete that was in the upper levels of the sport switched suddenly to the mid-sole cleats I would think that there would be the possibility of them actually loosing power and not do as well in the various races entered.  I suspect this because they have already trained their leg muscles to work a specific way, and have stronger portions of their muscles.  If they changed their stronger muscles will no longer be the ones putting forth an effort while riding, but the weaker (previously less used) muscles are now the main source of their power.  If this happens it could be a several year setback in their ability.

If anyone has used these type of cleats, and can tell of some feedback in the differences resulting please do.

http://www.trainingbible.com/joesblog/labels/cleat%20position.html