I posted on another thread about this...but I can't find it.
Anyway...I think there are times that spanking is acceptable. Not that spanking should be used in anger or frustration. Hitting in anger is abuse, whether the child misbehaved or not.
I told the story of the one time in my life that my father hit...and I deserved it. He had tried every thing else, but I was a stubburn, stupid teenager who refused to listen. The hit, not a spanking, but a back handed slap, got my attention and got his point across. He didn't do it in anger, he didn't do it out of frustration. I swear sometimes that he calculated it, as if he knew I wouldn't listen anyway. But, he didn't leave it at that. He cried and hugged me and implored me to not go down the wrong route that I was headed into. That happened about thirty years ago and I remember it as if it happened yesterday. Not the hit, not the pain, but I realized he did care, he did want the best for me. It made a deep impression (no pun intended) and it changed the way I respected my father forever.
Hitting smaller children without first trying to discipline is not acceptable however. I think spanking should be a last resort type thing. With most kids, you'll find a suitable punishment before you have to resort to spanking.