The very first book on .NET Gadgeteer, Simon Monk's "Getting Started With .NET Gadgeteer" is available for pre-order from O'Reilly Press and other booksellers. In addition to introducing core Gadgeteer concepts, it contains several project walkthroughs: a camera backup device, a game, a Web picture messenger and more.

See more at the book's Web site:  http://www.gadgeteerbook.com/home