I think as long as you aren't doing it for the purpose of physically abusing the child, spanking can be a very useful tool for out of control kids.
My mother hit us with whatever she could reach... spoons, spatulas, etc. I am one of 7 and none of us are cognitivly damaged or emotionally retarded. I think people overreact to the idea of spanking, and these are the same people you see at the grocery store trying to rationalize with a 3 year old.
In answer to all the scientific studies... well, science says that we really don't have the capability of understanding the underlying consequences of our actions until adolescence....
Sometimes the only way to correct a child, especially with dangerous behavior, like running out in the street, etc, is Pavlov's Theory.... (ring a bell, the dog salivates) You can train your children not to do something automatically because they know what the outcome will be.
And for those who say "we don't hit our friends and family", that is a crock... your JOB is to raise your children and teach them behavior and appropriateness, and right from wrong... your friends and family had their parents to do that... if their parents failed and they still do things that make you want to hit them... go get some friends that got spanked by their parents, I bet they will be more tolerable then the ones you have now!