The way it works is that you receive the book in the mail, you fill in a page with your thoughts on software craftsmanship, upload a picture of the page to the website, then you receive the address of the next person in line. Now, just go mail it. I was the first person to receive it, and I've held it for about 3 weeks. Today, though, I finally mailed it off to Jason Gorman.
The uploaded pictures of the filled-in pages can be viewed on the 'view the book' page (mine can be seen there, as well). It is a great idea, and I can't wait to see what other people write.