One of the challenge of developing WPF and Silverlight is manage your UI. Especially when developing LOB application, there are numbers of possibility which the application need to be extend to others modules in the future. In order to address this challenge, Microsoft introduce a practice known as Composite Application Guidance.
The first version of the Composite Application Guidance shows the code in C#. If you are VB developer like me, you are going to convert the code line by line. But the hassle is over, there is a VB version available for you.
You can download it here.