Personally I have no problem with hand-holding. But I do take offense to constant smooching and kissing in a public place, like, say, a queue line at Disneyland. Petting, long-sessions of kissing in public are inappropriate in my book, especially when I'm standing there approximately two feet away desperately searching for something innocuous to look at. I mean, what do I do? Should I join in in all the kissing?
To be honest I'm not a big fan of public displays of affection. I wouldn't make any rules regarding it but it feels a little in my face sometimes. I personally don't like that much constant physical contact. It feels like I'm seeing an advertisement or bragging sometimes. It's a personal quirk I guess.