Two theories floating around on the interwebs... that it was a publicity stunt for the author, who also listed two other newly published books on amazon, or that the FBI planted it as bait to catch real pedophiles. I really hope one of those explanations is true...
It does spark an interesting debate - I have worked at many bookstores over the years, starting when I was 16. I remember my first boss explaining to me that I could not let my personal feelings about a book affect my customer service - she used "The Anarchist Cookbook" as an example. She staged two different mock scenarios, one dealing with an irate customer who wanted the book immediately and we didn't have it in stock, and one with a customer who wanted the store shut down because we did have it in stock. It was a very interesting experience, and taught me a lot about perspective... and it was a lesson I needed several times over the years.
The most confrontational customer I ever dealt with was a woman who was irate that the store I worked in placed the "New Age" section right next to the "Christianity" section. She actually said "how dare you?!" and claimed that the new age books would poison the minds of the young Christians, and that she was offended that she had to pass by and look at them while she was searching for a bible. I am not making this up.
So that leads me to the question... even if we find a book morally reprehensible, and even if it promotes illegal activity, do we have the right to ban it? Does that impinge on our (collective) constitutional rights to freedom of speech and freedom of the press? Is it a slippery slope? Is a publisher being brave or stupid to print it? What is the bookseller's role? I think it's a very interesting debate.