I really really really enjoy kissing IRL, so I don't have a problem with it on screen. What I find interesting about movie kissing is the way it has evolved over the years from pressing closed lips together to open mouth, tongue action and so on. And remember the way the woman would lift one leg up behind her while kissing? Did any woman ever do that IRL? And the way the man would bend her over backwards while kissing her? It looked so uncomfortable.
In terms of pure entertainment, my favorite is from Galaxy Quest, where the guy is making out with the alien girl and her simulation device malfunctions briefly to reveal that she is actually a multi colored octopus like creature. He does a double take, shrugs, then continues kissing her.