I keep the cleats pretty much as far forward as they go for my commuter shoes (road shoe cleats are back a little further). I wear my shoes fairly loose to avoid any restriction/numbness, so when climbing out of the saddle, my feet slide forward a bit in the shoe, effectively moving the pedal to a position just in front of the ball of my foot. This is when the positioning of the cleat is most important (essentially in a sprinter position).

When just riding along, I'm not putting enough pressure on the bottom of my foot to really notice a difference where the cleat is positioned. It works for my riding style, but probably not for everyone.