I use a good bit of profanity, casually, usually for emphasis...my wife is from Jersey, so I hear F-bombs at home a lot. I tend to be a bit of a prude, so most of my friends swear more than I do.
I played in a group for a little while that was run by this nice mormon gentleman, in his home, with his wife and kids running around. I was amazed how much I had to censor myself so as to not be insulting to my host, or the little pixies' ears. I didn't mind, it was just a little shocking to me, and always made me lose my train of thought and fall out of character. I would get used to it in time.
One weekend everyone else was gone, and it was 'just the guys' playing in the house. I guess I relaxed a little too much, because after that session I got teased for having a potty mouth.