WFMU has posted a 1968 radio show of Shepherd telling the whole story.
Link
Via Boing-Boing
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http://en.wikipedia.org/wiki/Naked_Came_the_Stranger
The book was written by 25 authors who were frustrated that the books making top seller lists really only needed to offer stories about sex, and the sales would come.
So these 25 authors got together and purposely wrote the worst, saltiest piece of crap they could. Each author took one chapter, without really sharing with other authors what they were up to other than the basic premise (so there was not much consistency throughout the book). They even rewrote some sections which turned out to be too-well written.
It rocketed to #1, and eventually the authors came forward out of a sense of guilt from how much money they were making off of it.
Subsequently, the NY Times changed their procedure to only count 1 book per purchase.