I was in a conversation earlier today, where we talked about the familiar rating tools that you find in Amazon and frequently on internal website (rate this article). There are some big differences in rating services on a public website, like Amazon, and internal websites.
On Amazon, the review is something that you can reasonably assume other people will see and use to help decide whether to buy the book. There are millions of Amazon users, and even books that are way out on the long tail might get reviews. The review does not have any bearing on the content of the book for the next people to buy it. Reviewers have vested their time and energy in reading and responding to the book, much more so than they would for an article or report on the corporate website.
For an internal website, the biggest draw to the content is that there is a shared context of all the people visiting the content: People in the company generally have a desire to see the company do well and understand the culture. As such, while articles on corporate sites don't generally require time and energy to read, the value for the users of having the right information in them is much higher. The rating system should allow for direct feedback on the content so that it can be improved and republished. The other aspect is the shear scale. Most articles on internal sites get very few ratings; most of the ratings are 4 or 5 out of 5; and there is very little commentary. (I think this applies to external-facing website too. I don't know what would make me want to "rate this article" at a company website.)
The summary was: don't compare internal rating services to Amazon reviews. Rating systems should be used for continuous improvement of the content (and design) offered to the users.