Writing a book is hard, however, if you consider the amount of time you spend writing blog posts, using Wordpress to write a book makes a lot of sense. Check out my post on it:
Basically you can use posts as "chapters" and it allows for easy access. Plus you can use the private feature to hide them from visitors if you wish.
Would you ever use Wordpress to author a book? I'm currently trying it out with my memoir. (http://www.outstandingwriter.com/book)