for me its a consequence thing. i have 3 kiddies, 8, 5 & 2. We smack when we need to which isn't often at all. Its probably 6 months since our eldest has had one because we have other wyas to punish him for bad behaviour. He has the "ladder of certain doom" at the moment but it needs to change every month or so to keep him interested. In the past we have done things like making him clean the toilet or standing on the toilet for 15 mins. They all work but loose their effectiveness after a short time.
What i have found is that we have had to correct our children with a smack more between the ages of 3 & 5 than any other years as they simply don't recognise other punishments. Try telling a 3 year old to go to time out or clean the toilet, their only real consequence they remember & motivates them to behave nicely is a hot bottom.
I had a thought the oter day after watching the parenting show on TV, a small booklet with 25 different ways to punish without smacking or similar would give parents who can't think of other ways to correct their kids would be very helpful IMO.