I remember the first time I experienced Adaptive Cruise Control putting the brakes on some 11 or 12 years ago - my foot was hovering  right over the brake pedal (I'd been lent a £100k Lexus LS Hybrid Long Wheel Base complete with an £8k 'relaxation' upgrade on the rear seating).  Surprising how quickly one gets used to this sort of thing though. You can see the AEB in action on the video of Euro NCAP testing here (should start at beginning of AEB tests):