I have just recently began playing with this setting on my K20D. I have been using it combined with AF.C mode and am not sure yet, but I seem to be getting more keepers when not using it in AF.C, at least on my numpty around the house practice shots.
Nice to read it seems even better on the K7.
EDIT: Thought I would add, I have also been doing this in spray-n-pray more as well...it slows the the FPS but still, more of what I am getting are keepers. Since i have AF decoupled from the shutter button I just hold the AF button down while also holding the shutter down in order to keep AR spun up and activated. Of course for tripod shots no need for SR as a rule.