Evidently, there was a blogosphere and media freakout earlier this month over a study on the number of "swears," as my kids used to call them, in 40 YA books. Profanity in YA: Research, Assumption, and Feminism at Stacked is a very readable and interesting analysis of the study, "A Helluva Read": Profanity in Adolescent Literature. It covers what the study did and didn't do and the erroneous assumptions traditional and on-line media jumped to regarding it.
In reading some of the comments to the two posts I linked to, I noticed people writing that when profanity appears in teen books it reflects the reality of teen culture. I would agree with that. But I would also like to argue that the main reason to use profanity is to define character. Personally, I'm more interested in expressing something about the characters I'm creating than I am in making a general statement about any particular culture.
I'm a writer, Jim, not a sociologist!