wow this is a really interesting thread!
I never smack my kids. As a teacher, I can control 18 pre-schoolers without being physical, so I see no reason to smack my own! I agree that parents are role models, and need to teach through their own actions.
However, I do believe that some children do just need a smack, and verbal 'telling off' is not enough. kind of like in movies, when someone is being hysterical and then someone slaps them just to shock them out of it!
As for the partner doing things you don't agree with, that is difficult. My husband is chinese and i am english so we had very different upbringings. Normally if he does something i dont agree with, i ask him the reasons why he did it that way. If it sounds reasonable, I let it go, if not I will explain my thoughts and can usually talk him round to my way of thinking! (the fact that i have studied child development often works in my favour!) I would never do this in front of the kids though, as i think it is important that they see mummy and daddy as a unit who support each other, otherwise they will end up playing us off against each other!