Meganerd's right - a short, sharp shock is, sometimes, the last but only resort to show a child where the line in the sand is...
Some say that if you have to resort to being physical, then you're not doing it (parenthood) right; these are the same people who are either being ridden rough-shod over by their kids, or they don't have any.
I was hit by my parents on occasion, and I know I deserved it every time (and a lot of other times that they didn't know about too
) and it had nothing to do with abuse. A slap should be enough to get a child's undivided attention, so that you can impress on them your values...it shouldn't be aimed at hurting the child. Kids are happy to be shown what's right and what's not; they like knowing where that line is...
Just my 2p from a father of four happy children.