Let's consider. Amazon has all of our attention, for getting it, for having our one-click accounts all ready to be one-clicked. For getting the UI right and the experience right. They have reviews, of sorts, and you can kinda see how that could be expanded into a rudimentary trust network.
Alexa has lots of information. Alexa, you'll recall, had archives of web pages that we later came to know better in the form of the Internet Archive. And it did Related Links for a URL before Google did, with an accompanying place on the Alexa toolbar to rate site quality and get metainfo on the site itself.
Google, of course, has all of our love. Google is Google.
Now remember, Amazon bought Alexa a couple of years ago. So, what if you layer those Amazon features, and Amazon's UI, on top of the information of Alexa and the feature set of the Google API?
Answer: Alexa Web Search, the intersection of Amazon and Google. Complete with thumbnails of search results and an option to write a review of a site you find.