To calculate the overall star rating and percentage breakdown by star, we don’t use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyses reviews to verify trustworthiness.
Perennially popular Guinness Book of Records - BUT... it's the USA edition. This means (1) it's the size of a paperback novel, (2) it's printed on newspaper, (3) it's all black and white, and the pictures are just grimy black blobs.
Also, of course, at time of writing (July 2010) it's 5 years out of date. Clearly no-one is going to bother with this, and quite right too!!