the ''jacking points'' ie the sills, is actually incorrect. you should NEVER jack a car up on the sills. this is all forms of wrong, if i seen anyone jacking a car up on a sill i would seriously need to refrain from punching that person. a 'jacking point' refers to the safe lifting point for a 2 or 4 post ramp, where even force is applied across all 4 of the jacking points (oddly enough, this is demonstrated in matthews picture above.)
jacking the car up on a sill means that as you raise it, 1/2 of the weight of the vehicle is pushing upwards on a small bit of steel, when the weight of the car is pushing down on it at an angle. the only result that's going to happen is the bending of the metal itself. the sill itself is only reinforced vertically, at any other angle it's weak as hell and bends.
ONLY jack your car up on the control arm (wishbone) or the rear beam for non suspension work or if you simply wish to raise the vehicle onto axle stands to do suspension work : the chassis rail itself.