Book publishing as an arm of marketing has a long history and usually the end user is the winner. In this case we have some free programming ebooks from Microsoft for you to download.
Microsoft really does want Windows 8 to be a success so it has a arranged for a free ebook on the subject of app development:
This is a full 300 page book, and not a preview or extract edition.
Currently it is only available as a PDF but the website is promising EPUB and MOBI formats.
Slightly less useful as a free book, given the release of WP8, is:
Programming Windows Phone 7, by Charles Petzold
Similarly you might like
Moving to Microsoft Visual Studio 2010
but it is more likely that you are considering the move to 2012.
Let's hope that Microsoft make the later versions of both these books available in the near future.
Metro Revealed: Building Windows 8 apps with XAML and C#