UPDATE: Author of this book, Leslie Vail, has got a post on her blog (Dynamics Confessor Blogspot). Link now added here to her own post: Published at last! Developing Microsoft Dynamics GP Business Applications.
I had the privilege to be a part of the technical reviewing of this amazingly informative book: Developing Microsoft Dynamics GP Business Applications.
This book is penned by one of the most experienced GP personality and multiple times MVP, Leslie Vail. Packt Publishing has published this book.
I strongly recommend this book to all GP developers/consultants who would like to know how to develop anything with regards to Dynamics GP; be it a new feature addition, a feature modification or just a cosmetic enhancement.
Thanks Leslie Vail for this wonderfully written book with every single important concept being covered.