1) After working on the book for six months, I'd like to be able to follow up and ask you to contribute to the Kickstarter campaign if you like the book.
2) You are downloading an advance edition of a book that contains code that is likely to change. Within the next week or two, I will release an updated version. I'd like to be able to notify you when the update is available.
3) I am only giving the book away for free for one day, to promote the Kickstarter campaign. If you are willing to provide your email address in exchange for a free copy of the book I am grateful. If you are not, Michael Hartl offers an excellent introduction to Rails that does not require registration or an email address: