DRS is a retarded system because of the artificial, non-technical limitations imposed on it. Why can't the defending driver use it? Why is the boundary exactly 1 second and not any other value, and why can it be used in one specific part of the track which is determined by some arbitrary measure? It's idiotic, and doesn't add any true value to the sport. If we were to believe Alonso, and why wouldn't we, tyre management has a far more significant effect on an overtake for position, so why is DRS even there then?
KERS isn't quite as stupid, but the usage-left bar going slowly to nil and then magically going back to 100% again requires some serious suspension of disbelief. If the system is actually recovering something during the whole lap, it's only logical that the bar should rise accordingly and that it would be up to the driver to manage it such that there is enough left when it's needed for defending, an overtake or an in/outlap push.