Google started to show additional information for web pages that include reviews: their date and the rating. For now, this is still an experiment and you may not see the change in Google's search results.
Last year, Google enhanced the snippets for discussion boards and scientific papers, while extracting the published date from many web pages. Google is able to recognize the structure of a forum thread, find the number of posts and the date of the last post, detect the author of a scientific paper and extract the ratings from all kinds of web pages.
It's amazing to see how many useful details can be obtain from unstructured web pages without requiring a special markup.
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