I'm actually quite sure -- the reaction time of the control
unit should be less than the characteristic period of the
controlled system.
Think of it as a big pendulum which is subjected to rapid
kicks -- by applying kicks at different directions you can
keep pendulum at any angle.
Try that if the pendulum swings faster than you can kick 
Not that it is very useful for updating metrics, but you can
imagine a car radio which makes congestion announcements
fast enough, so as to load 101 and 280 equally (car here,
car there). Wait a second, that reminds me of something
--vadim
Vadim, are you shure about this?
Withouth the friction - what would you got this case? Very big pendulum,
isn't it?