I believe that people/couples should be considerate of those around them.
If we're with our friends, then most PDA (open-mouth kissing, playful groping, etc) is acceptable... to an extent. We don't do more than we ourselves would be comfortable seeing our friends do.
If we're in public, in the presence of strangers and children, we'll keep it rated G. Holding hands, hugging, closed-mouth kissing.