This is an extremely interesting article from The Economist called "Fair Comment: The internet: Books and other products sold by online retailers can attract thousands of reviews. Why are they worth reading—or writing?" Although the whole article is really worth reading, the bottom line of the article is that more reviews on sites like Amazon equate to more purchases, even if there are bad reviews. Once you get into the double digits of number of reviews, people are more willing to buy the product. And even when there are hundreds of reviews for a book, such as Harry Potter, people continue to post reviews and they apparently tend to have some effect (by sheer number, if nothing else) on the book being purchased. Actually, the study claims, a small number of poor reviews makes it more likely that an item will be purchased if there are a good number of reviews.
I have to wonder if people are more likely to buy a product with a lot of reviews because that product is just popular (thus the reason so many people have reviewed it, because it's popular and been read by a lot of people). It also makes me think about my book reviews on this blog. I often don't review books I read because I think, "This has been out so long and other people have already reviewed it." Although blogs are different from the attached product reviews the article discusses, I think it is relevant and makes me rethink my mindset some. I know there are books that I might not have thought too much about, but after I see many people have liked it and talked about it, it makes me want to read it and/or buy it. And I like to read reviews by people who tend to like the same books I do (at least when it comes to choosing my own books to read).