Amazon seems to be testing a new aggregated reviews feature, in beta phase only for now. The feature puts select quotes from reviews next to the Customer Reviews summary, you can see a screenshot here.
It’s not clear how Amazon is parsing the reviews to pull out these quotes, but it’s obviously an automated system. It appears to be selecting single whole sentences of between 10 and 20 words, based on (among other things) the reviewer’s ranking and the similarity of key words in that particular review to others for the product. So for example, if lots of reviewers mention a book’s “brilliant twist ending”, the system will select a review with that phrase and highlight it in this way.
The feature was live for a few hours earlier today (Friday April 20th) and now seems to have vanished again. Some people reported that it wasn’t entirely successful and was occasionally picking up spam reviews and mangled sentences. Still, the experiment is a useful indicator of where Amazon is thinking of taking its reviews system right now, although it might be a while yet before the new feature is up and running full time.