My dad was a very strict disciplinarian and spanked me a lot when I was little. It terrified and confused me because I often didn't feel I'd done anything wrong.
Spanking didn't teach me manners or discipline because I was a quiet and reserved kid and pretty well-mannered, but also far too contemptuous of authority to allow anyone to keep me "in line" (and I haven't changed much since then).
The one thing spanking did teach me was to hate and fear my dad, and to try to avoid him whenever possible. So we had a testy, combative relationship all through my years of growing up. We're better now, but there's still a certain distance between us and probably always will be.
So, I don't believe in spanking and would never do it to any kid of mine. Not that I have any kids, which may itself be another side effect of the whole spanking thing.