While Google announces new acquisitions almost daily (the universal library is fairly mindblowing), Amazon makes little improvements which you only notice later. For example, I just added Mike Davis' Ecology of Fear to my "Now Reading" sidebar, and went to grab the URL. You can now read the first sentence of the book, and get a list of the books Davis cites in his book (all hotlinked) and a list of books that cite Davis' book (also holinked). It's a minor improvement on the site, yet quite cool.