Well, my mom whooped me with wooden spoons, belts, and whatnot... but never an extension cord. I can't imagine being hit with a plastic coated wire... yeowch!
I don't see any problem with using corporal punishment when it's needed... but start the discipline with taking privileges away first... the law says all you have to do is provide food, clothing, shelter, and education. No law says you have to provide internet access, computer, phone, GameCube (or Xbox, etc)... strip his room of everything and let him earn it back as his grades increase.
However, that takes additional effort on the parents' part and it's so much easier for the parent to haul off and whoop the kid once and be done with it. People have become so damn lazy.