Personally, for the track I ride my cleats as far forward as they go, but I wouldn't have them much more further forward. My analogy of how this works is that you run on the balls of your feet (unless you own a pair of these shoes with too much heel padding, provoking heel strike). The natural way to run is on the balls of the feet (as I'm sure almost all barefoot runners would agree with), so why would it be different on a bike?
I do however put the cleats back a little for the road, the calves become the limiting factor for me if it's over an hour.