My 13 year old recently asked me for money for the school book fair, and mentioned something interesting: "I'm going to buy Eragon. All my friends are talking about it."
Now we've been big into J.K. Rowling and more recently Chris D'Lacey, and I am constantly bugging my kids about what they like (Ella Enchanted and Because of Winn Dixie were last year's household hits.) However, this was the first time my kid wanted to buy something that his friends had recommended. I asked him what they said about the book that got his interest.
His exact words: "I know it's about dragons. The guy who wrote it, Christopher Paolini, is a kid like us. They think that's cool. If it's good I want to get Eldest."
He knew the author's name -- another first. I have noticed Eragon being sold in the quarterly school book sale handouts since the book hit the BSL, and that's choice advertising. But I think word of mouth sells more books to kids than anything, and you can't buy that. They decide on their own whether they like you or not.
Now if we could just get adults to do that.