Never on purpose IYSWIM. I'm lucky that DD is, in general, a good kid. She has her moments, and can really push my buttons, but I deal with as calmly as possible.
I have a terrible temper - I'm a real screamer and shouter, just like my mum. I made a conscious decision NOT to be the same with DD so when I feel my anger bubbling up I walk away. I tell DD the truth, that she has pushed me too far and that I don't want to smack her, so am walking away. I tend to lock myself in the loo for a few minutes - although have been known to stay there for half an hour. I actually keep my iPod in there so I can plug myself in and not hear her if she carries on.
I think it works because of the time I did hit her
. I can't even say smack, as it really was a hit. She was about 4, was being a complete pain in the arse, was whingy, whining and rude over something ridiculous. She had thrown stuff at me and smashed a mug on the floor on purpose. I went upstairs and sat on the bed to get away from her. She followed me and whilst my eyes were closed clobbered me across the head and ear with a hairbrush. I reacted instinctively and hit out, catching her across the back and arm. It was a hard hit, left a red mark that lasted for an hour or so. It hurt her and scared the crap out of me.
It has never happened again, but DD and I both remember it. Neither of us would want to go there again. Taking myself out of the area is effective and a darn sight less dangerous than me losing control again.
So I don't agree with smacking as a punishment and don't like to see other children smacked - however, not all parents have tempers like mine. Some would be able to stop at a tap, I'm not convinced I would be, so don't do it.