Hold on, I'm going to do the (non)sensible thing here, and refer my initial opinions on this rather controversial ethical topic... over to a comedian's anecdote.
You see, children are stupid. Kind of an undisputable fact there; they haven't fully developed their minds. They need to learn lessons as they grow up, and it's a parent's job to guide their upbringing.
One of the important things to do is establish a child's respect for positions of authority, the first immediate one being that of a parent over a child. This is something they need to understand. Get this down, you'll be able to teach a kid any lesson and they will feel obligated to learn it and take it to heart.
If you can get them to wholly comprehend and respect this fact without resorting to any sort of physical reprimand, then good for you, that child is a really good kid and you should be oh so very proud.
I can personally assure you that that is not always the case.
My mom beat me as a kid, and I learned to respect her and the experiences she passed on to me . The occasional physical violence will drill straight into a child's mind who's in charge. Couple that with teaching them why they were punished, and they feel they learn something from a figure who knows better than them. It shouldn't take long for the little child to respect the adult's authority and wisdom. Naturally as a child grows older, they learn that adults aren't infallible. Let them comprehend that fact in due time. But while they are a kid, let them be subject to a physical reprimand when necessary. Also tell them what it is they did wrong, and (the important part) why it was wrong. Each instance is a two part mental exercise for the kid's developing mind, both in cause and effect relationships and mental association.
I'm eighteen now, and I got my Associate's degree a year ago because my mother encouraged me to go for it. So I did. Now here's the important bit: I did it because I wanted to. I didn't do it to appease some authority I feared, I did it because my mother instilled the values of education and learning into me as a kid. I put genuine thought into the option of pursuing an early college education, saw the benefits from it, and made the directive my own. It was merely her suggestion, but it was my choice.
Now let me tell you about my brother. We have always shared a room and have had pretty symmetrical upbringings when we were younger. The only key difference is that psychiatrists convinced my mother not to beat him like she did with me. He's eleven months younger than me and barely passing high school. He has little respect for people (including my parents) and no respect for property, whether it be his belongings or others'. He is, as I type, shirtless and trash talking on Modern Warfare over Xbox LIVE a couple feet away from me.
I think I have reasonable grounds to form the opinion that, yes, I do think it makes a difference whether or not you are willing to spank your kids to teach them a lesson. A decent spanking lasts for a few minutes. The proper lesson instilled early enough lasts forever.
...Wow, I didn't expect to go on for that long.