I really like PDA, especially with a gay couple. When a gay couple isn't afraid to show some affection in public, I think it's adorable. Just the other day I was holding hands down the street with a guy so I definitely am not uncomfortable doing it. I think it is fine and sweet when straight couples do it as well.
Now I think it's possible for PDA to go overboard. It can definitely go over the top, but it doesn't really bother me if it does. I have recently made out with this guy in a bar, restaurant, and on a street corner so I can't really say much about it being overboard (whoops!)