When I test drove a Boxster... it left the dealership with about 5km and came back with over 25km because the dealer drove us to a nice out of the way road. Then I ordered one in the color that I wanted, and mine had barely 1km on it when I took delivery. The way I look at it, that's 20km less break-in period for that Boxter's owner
My Boxster rev'ed smoother after the first 1000km. The break-in period really does make a difference. I don't know what you mean by a jerk when you press the throttle, however I also feel a slight shake when starting or turning off the car... it is a horizontally opposed engine, so the weight of the pistons shift left-right.