Well, despite my aversion to this rather icky type of display, I remember that I was, admittedly, quite enchanted by same on my first visit to Paris, many years ago and counting. Weaned on various nouvelle vague films featuring Jeanne Moreau and/or the late Gérard (sigh) Philipe, but coming from the basically puritanical U.S., I was thrilled by my various glimpses of couples embracing and locking lips on virtually every street corner or under every tree in the various parcs. It was indeed "just like the movies." My romantic phase could last only just so long, however. What looked—or maybe even still looks—great in Paris or Rome just doesn't cut it here in NYC, especially if you're doing it while sitting in front of me at the theater. Like many another bodily function, it just doesn't translate into public behavior. I'm allowing for the greeting of a loved one at an airport or similar situation, but keep it short or get a room!
A couple of people who post on "Rex Parker's" delightful NYT crossword blog seem to agree with me. It's like a lot of other behavior that pays no attention to the sensibilities of others, e.g., not cleaning up your dog's poop or discarding rubbish in the street instead of in a bin. In the subway the other evening, a person (who looked out of it anyway) threw rubbish on the train tracks even though he was sitting right next to a rubbish bin. Well, if you want to live in the Big City, you have to put up with a certain amount of unattractive—or even illegal—behavior, but I do draw the line at PDA.
As far as Paris is concerned, it does have its reputation to live up to. I'm reminded of a scene in Cyrano de Bergerac in the Brian Hooker translation. Cyrano is trying to detain the Comte de Guiche from entering Roxane's house while she and Christian are being married. Cyrano claims to have recently fallen from the moon and not to know where he is. The Comte, after many attempts to get past Cyrano, blurts out: "A lady is waiting!" Cyrano replies: "Ah! So this is Paris!"