When one of your children does something really bad (e.g. hitting a sibling, or general nastiness to them), do you just take them to one side and have a little chat, or is, just perhaps, a more relevant punishment more appropriate. And I'm not talking about nasty stuff (belt etc), just simple smacking. It's used as the ultimate deterrent in our house, and as a result we have two well behaved and courteous children, who are almost never have to be punished with this ultimate sanction - because they KNOW THERE IS ONE. (For example, the 8 year old has been smacked about 4 times in his life, the 4 year old about the same - he's a bit naughtier). Using this ultimate sanction more often would negate it's usefulness, and most of the time, talking does the trick.
On the other hand, my brothers children, with a child psychologist as a mother, who have no ultimate sanction like smacking (a stiff talking to and a trip to the naughty step is about it) are atrociously behaved.
Just my opinion of course, from my own experience, and I certainly wouldn't condone excessive corporal punishment.