I'm still really on the fence about it with my daughter. She's got a few years before it becomes a real question.
On one hand, I definitely remember the lessons I learned that were punctuated by spankings (don't lie, don't wander into the street), but on the other hand corporal punishment does have a negative stigma for being old fashioned. I just can't personally vouch for the efficacy of other methods of punishment.
There is definitely a line between what is acceptable and what is excessive though. Is never use a belt or any such whipping tool, for instance, but an open palm (or wooden spoon in my case) on the bottom doesn't seem nearly as harsh.