I've seen this lots of places, but most recently at Ms. Bond's journal.

1. Grab the nearest book.
2. Open the book to page 23.
3. Find the fifth sentence.
4. Post the text of the sentence in your journal along with these instructions.

Mine is: "...pillowcase, baring her entire back, her skin pale as moths'..." Actually, that's the fifth *line*, but since the fifth actual sentence is "Perfect." I went with it. I should note that since I'm at work, this is surprisingly mild. The book is Taboo: Forbidden Fantasies for Couples, edited by Violet Blue. Ms. Blue edits a mean erotic anthology, btw, for those of you who like that kind of thing.