Microsoft Press has finally made the epub and mobi versions of this free ebook available. You can go to the link to download the format that works for you; pdf, mobi, epub. The link also contains links to the companion content.
This should prove to be a great resource for those wanting to do Windows 8 applications. Of course there are other ways of doing it; C# with XAML for example, but this version will probably appeal to most people.