Amazon reviews: Helpful or what?

I rarely look at Amazon reviews until I've read the book. After I've finished a book, I am curious to see whether—and how—other readers agree with my opinion and to learn why—and how—we disagree. This goes for whether I enjoyed the book or not. And I'm particularly interested in the top and bottom ratings. What is it about a book I thought was trash that other readers loved? And what is it about a book I loved (including books I've written) that some readers hated?

I've just finished a mystery by a debut author that I thought was extraordinarily weak. (The moment a character says, "I'll tell you [some key piece of information] in the morning," you know the next chapter will begin with the protagonist finding the character's cooling body.) I went to Amazon and looked at the 15 or 20 one-star reviews. I tended to agree with most of them including the person who wanted to know how a commercial publisher could have published such a waste of innocent trees. Interestingly, most of these critics wrote more than a one- or two-sentence dismissal of the book; they tried to suggest exactly why they did not care for it.

Which makes the more than 100 five-star reviews even more interesting. Without doing an actual count, it appears that the majority for this book are brief, generic, and essentially useless: "Thoroughly enjoyed the book." "Great read." "No plot holes."  "Great book." "Couldn't put it down." "Story was interesting." "Will look for the author's next book."

These, of course, tell you virtually nothing about the book, why the reader enjoyed it, or what she enjoyed about it. They are, in fact, all-purpose blurbs one could slap on any novel. Because there are so many of them and because they seem to follow a similar pattern, a cynical person might suspect they are not the considered opinions of readers who actually read the book. (I'm ignoring the whole issue of friends promoting friends' books.)

I am shocked! Shocked, I tell you! If you cannot trust the views of the people who post their views on Amazon, who can you trust?

My suggestion? Don't read the reviews until you've read the book.