I can count on one hand the number of times I have smacked DD. And only when she had ignored several other methods and was doing something that absolutely couldn't be allowed to continue, such as running out into carparks or other such dangerous behaviour. I hated doing it and felt crap every time, but it worked for the short period before she was able to understand my reasoning with her.

The majority of the time I'd use the stern "mummy voice" which was enough, otherwise we'd have other consequences like loss of favourite toy for specified length of time, time in bedroom etc. Tantrums were interesting and depended on the reason for the tantrum - overtired and so on weren't really her fault so I'd do what I could to calm her then rectify the problem. She never really did the shopping centre tantie after the first couple of times it got met with an amused "it's not going to work" and continuing about our business. Mind you, when she was well behaved she'd get a thankyou and occasionally (but not every time) a treat.