Amazon: Search Inside the Book

"Search Inside the Book allows you to search millions of pages to find exactly the book you want to buy. Now instead of just displaying books whose title, author, or publisher-provided keywords match your search terms, your search results will surface titles based on every word inside the book."

And here’s an interesting detail: "If you are a registered, recognized Amazon.com customer, you will go directly to the page you selected. If you are not a recognized customer, we will ask you to sign in or create an Amazon.com account (if you’re not already a customer). Once you have signed in or set up an account with us, we’ll take you directly to the page you selected."
Amazon deems the feature significant enough to use it as a way to register if they’re not already customers. The official reason is to protect it from bots, but a registered user is also one step closer to becoming a customer. Here’s the FAQ for publishers.
Update: The Great Library of Amazonia.
10/26/03: Another NY Times v Tasini? Amazon’s Book Search Hits a Snag.
11/02/03 update: The Amazoning of Google? Search Firm Looks for Book Content.