I read two books in a row where the swearing was terribly forced and unnatural. It occurs to me there just might be a job opportunity for someone who could let authors know whether or not they have the skill set to write characters who have a penchant for stringing together scads of invective.
That reminds me that I'm also not at all a fan of dialogue that mixes real-world profanity with curses to fictional deities. "By <insert fictional deity>'s f*****g <insert fictional deity's body part>!"