By participating in beta exams, you have the opportunity to provide the Microsoft Certification program with feedback about exam content. Having participated in the development process of these exams (including 71-564 below!), I know they depend on the contributions of experienced IT professionals and developers to improve and maintain the value of Microsoft certifications. But hurry fast, these spots don't last long.
Exam 71-564: Pro: Designing and Developing ASP.NET Applications Using the Microsoft® .NET Framework 3.5
Exam 71-565: Pro: Designing and Developing Enterprise Applications Using the Microsoft® .NET Framework 3.5