I had a co-worker who everyone thought was a great, progressive, parent. She bought her five year old a $300 comforter set, and a week later, the little girl got into a bottle of her mother's nail polish and got it all over the comforter. The mother didn't talk to the daughter for a solid week.
Apart from the stupidity of buying a five year old such an expensive comforter set (and this was twenty years ago, when $300 was a lot more than it is now), I think that giving a five year old the silent treatment is a lot more cruel than giving her a swat on the behind.
As I said early in this thread, spankings didn't bother me. They did my sister, but then my sister witnessed a lot of violence before I was born. And my mother's *words as weapons* tactics were harder on my sister than they were on me also.
Really, it depends so much on the individual child, how they will react, what kind of impact it will have. When my nephew was little, I gave him a swat on the behind a few times when he was having temper tantrums. In stopped doing that because it had zero effect on him. Then one time when he was being a really miserable little beast, I told him that I wouldn't hear or see him until he started behaving. He continued acting up, I ignored him completely, and then suddenly he was panic stricken - he started crying and tugging on my arm, saying "Mause! Mause! I'm here! I'm here! Can't you see me?!" I reassured him right away. But that's the occasion that bothers me to this day, not any of the swats on the behind. I didn't mean to scare him like that.