1. I thought about using a 3D mockup of the eBook, but I figured it was a little cheesy. After all, it's a book, people know what it looks like. I know, I know, that's not how you sell stuff…
2. I made the title look like a button on purpose since the book is about user interfaces. Probably not the greatest idea I've had…
3. That's actually not a close icon, but an "expand" icon. You can just click anywhere to close the lightbox
4. This is an easter egg, so I didn't want to make it too easy. Seems like you found out anyway :)
I'm definitely open to criticism. For my defense, I should say that I design my own stuff differently than I would design for a client. So I'm willing to give up a couple sales if I can inject some more personality in the design.