I've gotten so used to swearing that it really does not bother me anymore. I hear kids as young as 6 swearing worst than a punk rocker. Swearing in books just gives you an idea how angry or ignorant someone is so you get a better pictures as not everyone has the same vocabulary.
The media has made any kind of profanity easy to digest. When someone says some colorful words it does not have the impact that I'm expecting it to have. I must be desensitized. When I read it the effect is even less. If it is used often all it does is shows me that the character or author lacks more thoughtful ways of expressing what they want to communicate.