David Pallmann was first to have an Indigo book out in the public. See http://www.microsoft.com/MSPress/books/7703.asp for details.

Two sample chapters are available on the MSDN web:

• The Programming Model. http://msdn.microsoft.com/Longhorn/default.aspx?pull=/library/en-us/dnlong/html/progindigoch3.asp
• Contracts. http://msdn.microsoft.com/Longhorn/default.aspx?pull=/library/en-us/dnlong/html/progindigoch5.asp

I'm halfway through the book and so far its well worth the money! The book is more of a how-to book than a reference book, but for a first book on Indigo that is just right!

Unfortunately the book has some minor flaws (like typos and plain errors) which makes it necessary to look up details in the SDK documentation from time to time instead of just reading the book.

I'll update this post with a resume of the book.