Holding hands is fine, in fact, it tells me the woman is clearly taken. What I do object to is the face sucking, thing for ages in a completely public place...or more importantly, in my vision that I can't look away from (one such scenario, in the cinema, so I either don't see the film or watch it with two people directly in front of me having a face sucking contest).
I reckon the things I don't like in public are displays of erotic affection. The all-out, french-kiss, snog, I deem a display of erotic affection. The hug, I deem emotional. Erotic affection is fine behind closed doors, emotional is fine anywhere. It basically boils down to that for me...