THE point of books is to combat loneliness,” David Foster Wallace observes near the beginning of “Although of Course You End Up Becoming Yourself,” David Lipsky’s recently published, book-length interview with him. If you happen to be reading the book on the Kindle from Amazon, Mr. Wallace’s observation has an extra emphasis: a dotted underline running below the phrase. Not because Mr. Wallace or Mr. Lipsky felt that the point was worth stressing, but because a dozen or so other readers have highlighted the passage on their Kindles, making it one of the more “popular” passages in the book. Amazon calls this new feature “popular highlights.” It may sound innocuous enough, but it augurs even bigger changes to come.