You can now watch John Papa's PDC 2010 session titled "Kung Fu Silverlight: Tips and Architectural Patterns and Practices." Here's the summary of the session:
Learn about the rewards of using RIA Services together with development patterns, such as the Service Providers, Single Responsibility pattern, Commanding, user Interactions, Messaging, ChildWindows, Design Time Data, Testing, and developing using Model-View-ViewModel (MVVM) pattern, to build Silverlight and Windows Phone apps. Hear the top tips you need to know for building data driven Silverlight apps that solve real world problems.
More Info: Kung Fu Silverlight at PDC 2010