You may not think of Amazon as a Search Engine, but of course it is on many levels.
Amazon once allowed users to access something called SIPs, or statistically improbable phrases in any book, which got the essence of a book across (thus, SIPs of Karl Marx's "Labor" would be "average social labour," "Labour fund," or "abstract human labour.") Capitalized Phrases, on the other hand, were people, places, things or topics most frequenlty mentioned (such as the word "time" in T.S. Eliot's "Collected Poems."
What was cool about these features was that they had no commercial value (or not enough commercial value).
Today, according to Grafton, these features have been phased out in favor of the ubiquitous customer-generated content (tags, reviews, etc.) that help monetize the product. It's only natural for a giant of industry to have changed its course in favor of monetization (I think), but Grafton makes a good case for mourning the transition.