I've noticed that almost all our current cookbook reviews have notations that X number of people found the review usefull. As a reviewer, it's good for my ego that people find my stuff useful. But, personally, I find that information, of itself, useless. If you found a review useful (or, contrary, found it less than useful) the rest of us can learn something by hearing your reasoning. In other words, whether you like or dislike a book, or the review of it, your opinion is valuable. I, for one, would rather you posted comments then merely press the usefullness button. It's not hard. While you're on the book's main page just click on the "write a review" button. The rest is no different than posting a response on a forum thread.