My father, before he died, used to curse like a sailor and then, there are people who don't curse at all. While I do use an occasional curse word, but for me, it depends on a great deal of things.
1. The age group - if you are talking about a young child, use creative curse words or even older curse words as they are mostly nonsense these days. They no longer hold the OMG, that it used to, and that leads me to the next thing that I take into consideration.
2. The country - Sometimes, people have curse words that do not mean anything in your language or culture, so I take that into consideration.
3. The character personality - The personality of the character is very important, so if you have a nice girl and suddenly, she starts belting out curse words like a sailor, you might reconsider the ways she speaks.
4. The sort of game you are creating - If you have a mature sort of game in the inner city, I would imagine that you would hear quite a bit of cursing, and even in a horror game, you might hear a little cursing. Of course, this goes into the whole know your character discussion.
5. Treat cursing, even if it's nonsense, like you would salt. It adds flavor, but it shouldn't be the whole flavor of your game.
Strangely enough, I curse when really upset, but when I make my game, I rarely use curse words.

So, go figure, right? I am not against cursing, because I am sort of realistic when it comes to life. Yes, there is going to be cursing, but you don't have to draw attention to it. It's just about common sense about how much and if you should include cursing.