Punishment isn't always a negative manner, despite people thinking that punishment is an extreme action from time to time. If your child is not disciplined at an early age, they have nothing to fear really. Who's to oppose their actions, or know their rights from wrongs exactly until older (even then, it's to late at that point for most who've grown used to getting away with it.)
Spanking a child seems unpleasant, especially if done in a way that seems quite violent (like using a belt- don't ever use a belt. That's a bit much to me personally) however it's one of the many steps to ensure the child knows there are consequences to his/her own actions. Being to harsh or inflicting them constantly is also bad, for it makes them understand that they'll always get the short end of the stick with beatings. I am not a parent, but knowing how I was raised I can say the punishment necessary depends on the family and methods.
So if a spanking works, leave it at that and when the child behaves or does right- reward them. If they do wrong, repeat the simple punishment to help them know not to do it, and yes they can forget this easily and continue onward so you may be left thinking, "Spanking isn't working, what to do?" Simple, warn the child that you shall strip them of their possessions. Once they clearly know they are in for it, remind them with words to behave or else. Words are power, actions should be a last resort but never overdo it. As for my opinion on spanking.. if the child ignores the adult's request to behave or settle- then a spanking on the hand should suffice. If not, the butt.. if not that, then proceed to taking away what they enjoy for a short time until they understand.
I'd tell my son or daughter somday,
"When your PSP is missing from your desk along with your Xbox 360 and computer.. you have my permission to cry."