Good article with a few points that affiliates can learn from:

According to Strain-Seymour, implementing product reviews can deliver a lift in traffic from SEO and social sites, lift in conversions, higher average order value, and a reduction in product returns. Product reviews are also helpful for providing information thatís missing from product descriptions.

But to have a successful product review program, you have to get your customers to actually come back and review products. The best way to achieve that is to make a point to ask them outright. Only the truly passionate (often upset) customers will respond on their own.