Google has quietly added support for book reviews rich snippets with the data highlighter tool.
Pierre Far from Google announced it on his Google+ page saying “you can now use Data Highlighter to tell us about pages on your site that have book reviews.” That means you can now mark up pages with this tool to communicate the part of the page that have items such as title, author, reviews, and reader ratings.
You can learn more about the feature over here.
Google added several data types to the data highlighter tool in May, and this update brings up to eight total data types now supported: