For things like books, I also find that reading the middling reviews often gives the best S/N ratio. It weeds out the fanboys and weeds out those who were clearly not the audience for the book (or just have some ax to grind). You're more likely to get the "I really love this author in general but I didn't care for this book because 1.) 2.) 3.)."

Agreed. For products in Amazon above a certain star threshold (say, 3+), I evaluate given the shape of the review histogram, particularly minimizing the size of the bump down at 1-star and 2-star.