I've had my ST a little over a month now. Typically, I push the car harder through the twisties than in a straight line, and I've yet to feel the system influencing my decisions. Could be that I'm not pushing hard enough, or maybe Ford has done a very good job with the tuning.
I like that the system resets to full assist each time the car is started, and does not remain in unassisted mode should I decide to disengage it.
Primarily because my wife will occasionally be driving the car.