If you're looking for bargains or out-of-print titles this is a fantastic service. But is it creating a new market that will damage the book trade?
An article in the New York Times (free registration required) suggests that publishers are starting to worry.
"We think it's not good for the industry and it has an effect, but we can't measure it," said Paul Aiken, executive director of the Authors Guild, a trade group. "There has always been used-book sales, but it's always been a background noise sort of thing. Now it's right there next to the new book on Amazon."