Finally the “MCTS: Microsoft Silverlight 4 Development (70-506) Certification Guide” book authored by Johnny Tordgeman is available in the market. I was the Technical Reviewer of this book along with Evan Hutnick, who works as a Developer Evangelist at Telerik.
In short, this book will provide all that you need to know to pass the Microsoft Silverlight 4 dev exam (70-506). Find more about this book and publisher link to buy it online.