She's talking about the growing market online for used books. I will admit I buy a lot of older books at half.com. When it comes to newer books, if they are available at both my local bookstore and Amazon, I will pay the extra couple of bucks that it usually costs to buy local. (And the author actually gets a little more in royalties in well, as Amazon is considered a "deep discounter."
This piece in the New York Times looks at all the considerations of where and when you buy books.