I heard the "constant use" FAA regulation at SEA with regards to the big Xray machines used for checked baggage. They know that they don't have the capacity to screen everything yet, so they at least want the machines to be used constantly. It would be pretty dumb for them to sit idle while unscreened luggage was loaded onto the aircraft.
More generally, I've found security to be improving at SEA both in efficiency and apparent effectiveness. I've been selected for a couple searches at the gate lately and they were far, far more thorough and professional than the ones I had last Fall.