However! I did play in a star wars game for a little bit, where the DM proclaimed, hey, there's no swearing in star wars. Nobody there was offended by swearing or anything, it was just a style issue.
Seriously, profanity does happen in our games, though we've vastly curbed it since one player's 11-year-old son now plays with us. The NPC's still have the occasional swear to emphasize what kind of character he is or not.
On the notion of what sorts of swear words are "appropriate" to a D&D setting -- it's kind of surprising how consistent swear words are across cultures. It's generally sex, heredity or defecation. There's a few wacky ones in any culture, but they pretty much all have counterparts to the "F" and "S" words.
And a phrase like, "Kiss my round, firm and perfectly smooth a**," has pretty much the same meaning in any culture.
That last was a favourite of one of my NPCs. She had a pretty high opinion of her own ass-ets.
It's not as if it is a constant stream of obscenities, but we've been know to express ourselves through use of (as Mr. Spock put it) colorful metaphors.
I've had characters that couldn't utter a sentance without profanity, usually modern profanity, cause I do speak english, sometimes american, sometimes british, and any aussie speak I can happen to think of at the time, cause those guys talk crazy. My father worked docks as an impressionable youth, and he still talks like it, so I can blaim it on him.
Swearing at the gaming table doesn't bother me much as long as my kids aren't around.
I got a letter from my son's teacher the other day regarding some of the kids in his second grade class were sending vulgar messages on the computers there. I called her for more info, apparently my son was not involved (confirmed after the thorough grilling I gave him) after I got off the phone with her I asked him what kinds of words were on the computers and I gotta tell ya, hearing those words come out of his mouth really made my teeth curl. My wife and I both try to watch our language around our kids but what they take home from school we could never top. Its a shame, but what can you do but reaffirm your values to your kids and hope for the best. Thank goodness the boy has a pretty damn good head on his shoulders. I attribute that to me of course.
We don't talk any differently than we would normally. It's not unusual to hear a cuss word (sometimes of the extra-dirty variety), but it's not like we curse with every other word.