Personally, no I haven't. But I did witness a friend do it once. We were at the school gates (yes it was in public!) and the child was being just hideous. And then he said something, I can't for the life of me think what it was, but I know I gasped so it must have been really bad.
And then she slapped him round the face. Now usually I would have been horrified, but I was there, I was witnessing it and I kind of 'understood'. I was still horrified, I suppose, but also really felt for her.
You could hear a pin drop of course as everyone else looked on. She was distraught at what she had done, she apologised. But so did the child.
I think he learnt that his mum has her limits, and he had just reached them.
That was 6 years ago, and I know from that point on she worked really hard on disciplining effectively so they never got to that point again.
So I think what I am saying is of course it is not right to slap your child in the face. BUT, it is not the end of the world, if handled correctly. I think you need to talk to your DS about both of yours behaviour, so you can both move on.