I'm not one for doing it... i see ppl hitting their kids and i want to spit. however, there is a time and place for it. When my son was 12-15 months, he loved to stick his fingers in electrical sockets. I would quickly slap his hand down. no pain, just a small swat. he didn't understand the words I said back then - no concept of how electricity would hurt him. Too young for time out. no other way to prevent it.
I only had to do it 3-4 timess and to this day he avoids sockets. more of a sting with the slap, you know? Today at almost 3 years old, I find time out is fine for most things.