A recent Bazaarvoice study in the UK found that 94% of respondents said that they posted product review to help other customers make smart product choice decisions. Furthermore, 82% of those surveyed said that they were also motivated to help companies make better decisions about which products to offer. Te study also confirmed that most reviews are positive; 86% of UK reviewers said they left positive feedback while 11% said their comments were equally split between positive and negative. This confirms what Bazaarvoice has observed in its ratings J-Curve (above).
While product reviews are undoubtedly helpful, I am, personally, more influenced by what people do that by what they say - Amazon's "What Do Customers Ultimately Buy After Viewing This Item?"for example.