I was smacked but personally i wouldnt smack my children.
I remember the shame I felt as a child being smacked and i really wouldnt want to inflict that feeling on a child of mine. The result of the smack worked in that i behaved myself but i dont think the feelings it left me with were positive.
I personally feel there are more effective and less harmful (psychologically and physically) ways of disciplining a child such as denial of certain treats, naughty step etc etc.
I saw an interesting program on it once and they compared childhood to old age and how certain old people "misbehave" due to mental deterioration which can be compared to the immaturity of a child, and you wouldnt dream of smacking an elderly person so why is it ok to smack a child?
I have to say that got me thinking and i do agree with it. I think that smacking shows a loss of control on the part of the parent rather than being a constructive discipline tool.