It's so seamlessly interwoven with the rest of Google, you might click on the Books option on the Google pull down menu and not realize it's now part search engine, part retail establishment.
People have been trumpeting Google as a game-changer, but if you ask me, in some ways Google ebooks look backward. That's because a significant percentage of the older books are available only as PDFs. They are, in a way, digital pictures of print books. You can tell because when you click on the book icon, the description page has a note above the buy button that says “Better for larger screens.” This is your clue that the fonts cannot be manipulated because the book is really just a PDF. Also, I don't see the Google ebookstore as radically different from the Amazon implementation of Kindle books. I now have a Google ebooks account page with one paid book and two free books on it. I have a Kindle account page with hundreds of books, both free and paid for, on it. Both of them offer me the ability to download to my PC or to a host of e-reading devices. I have a very similar page on Fictionwise and on O'Reilly. Google is just not that terribly different except they have more books because of the scanned older books.
In fact, for me, the biggest change Google ebooks has caused is that after more than a decade of having a Google ”account,” Google finally knows my address and credit card number. It seems to me that it's Google that's changing, not the game.
Washington Post coverage
Amazon's response: Kindle editions?, aka Amazon for the web