And they had to get a sizable amount of other people to truly care about the thing enough to spend lots of their spare time dicking around on it. Reddit, Amazon, Facebook, HN, Wikipedia, and Twitter depend on unimaginable amounts of hours spent by volunteers all over the world who get $0 for contributing the actual content and camraderie, which really is almost the entire value (except the case of Amazon, where it's only a pretty big part).
Are you referring to reviews on Amazon? Are those really that big of a part of their business? I rarely read them, personally. I just assume they are gamed.
The whole recommendations engine is based on user participation. Amazon naturally collects tons of data about their users, and they probably wouldn't be happy to lose this data. If you were the only user of Amazon, it wouldn't work nearly as well. I would think that features like "other users also bought," the thing that pairs up books into relevant groups, "Listomania," and so on, were crucial to Amazon's success.
And yeah, I do think the reviews are quite important to Amazon. A book with 4.5 stars and some intelligent good reviews must be good business for Amazon, don't you think? Even if some people are skeptical of reviews, they are probably much better than most other types of advertising.
