I found this link to a NYT article  about authors buying five-star reviews in today’s Galleycat (9/3/12). 

The article in the New York Times is worth every reader’s attention. One of the issues covered concerns negative reviews, or one-star reviews, a la Amazon. The fact that Bookin’ with Sunny generally does not publish negative reviews does not mean we think every book is perfect. We read a wide variety of titles and pass on an equally wide variety of titles. We choose to put in the time and effort writing reviews only if  we believe those books are worth a reader’s time and/or money. Each reviewer has their favorite genres and each brings something of themselves to every review. Our reviews do not make use of stars or any other image-based rating. Our reviews simply talk about the book (without retelling the story) and the writing and what we think of it.

A reader or possible book purchaser who goes to Amazon to see what other readers think, now has to worry about whether or not that review has been paid for, especially those five starred reviews.                     -s.s.