UPDATE: There will be a fourth part that discusses the add/remove facility through RIA Services. Look for it soon at a blog near you.
In the first part of this series, I looked at how WCF RIA Services can work in an MVVM architecture. In the second part, I looked at how you could use the Managed Extensibility Framework (MEF) to aid in composing an MVVM application. Now comes the third and last part of the series. In this part, I will focus on some common problems integrating MVVM and composed user interfaces (that are common to most of these situations, not just using WCF RIA Services). I will show you some refactoring of the MEF design from last article as well as show you how using a framework (I used Laurent Bugnion‘s MVVM Light framework (v3 Alpha)) can help you smooth out the rough edges of implementing MVVM.
from Shawn Wildermuth more here