"Since its release in 2007, the last volume of the Harry Potter series, Harry Potter and the Deathly Hallows, has garnered 3,286 reviews from Amazon.com customers. While response has been overwhelmingly positive for the book, several hundred Amazon customers rated the book as mediocre or worse.
Because of a very subtle yet clever feature, Amazon makes the best of both the positive and negative reviews easy to find. And that feature, based on our calculations, is responsible for more than $2,700,000,000 of new revenue for Amazon every year. Not bad for what is essentially a simple question: "Was this review helpful to you?"
The Problem with Chronology
Amazon had reviews from the very first day. It's always been a feature that customers love. (Many non-customers talk about how they check out the reviews on Amazon first, then buy the product someplace else.)
Initially, the review system was purely chronological. The designers didn't account for users entering hundreds or thousands of reviews.
Interestingly, only a fringe portion of the audience writes reviews. For example, while Harry Potter and the Deathly Hallows has more than 3,000 reviews, our calculations indicate Amazon sold more than 4,000,000 copies of the book. That's 0.075% or only one out of every 1,300 purchasers that took the time to write a review.
For small numbers, chronology works just fine. However, it quickly becomes unmanageable. (For example, anyone who discovers an established blog may feel they've come in at the middle of a conversation, since only the most recent topics are presented first. It seems as if the writer assumed the readers had read everything from the beginning.)
The problem came with the eleventh review. Since the product page only showed ten on the first page, the eleventh pushed the earliest review onto a different page. This worked fine as long as every new review was better than the existing ones.
But that wasn't happening. Newer reviews often had a what-he-said vibe to them, echoing the sentiments of the well-written reviews, while, at the same time pushing them out of the reader's view." (Continued via UIE, Jared Spool) [Usability Resources]