The book is published at Leanpub and is available in three formats: PDF, MOBI (for Kindle) and EPUB (for iPad). Updates for the book are free. So when new Grails Goodness blog posts will be added to the book you will get those updates for free.
It is also possible to buy a Groovy and Grails Goodness Notebooks bundle. This bundle contains the Groovy and Grails Goodness Notebook books.
I hope you will enjoy the book and I will keep it up-to-date with new content when I publish new Grails Goodness blog posts.