The great thing about Amazon's unchecked growth is the open door it creates for authors who cannot seem to lock down the precious shelf space of bookstores. And now more people than ever are shopping online, especially for books.
Typically, book release and promotion parties are done at an offline site such as a library or bookstore, even the home of a friend of the author. Now, more authors are doing online launch parties with purchase links set up all over the place (friends' blogs, websites and Twitter accounts). No need to tell you what this does to Google rankings for you and your own sites. That's why online launches shouldn't be overlooked by an author who wants to sell a lot of books.