Do you use the MVVM pattern in your Silverlight and WPF Projects?

The term MVVM means Model-View-ViewModel design pattern. This pattern is an adaptation of the MVC and MVP patterns in which the view model provides a data model and behavior to the view but allows the view to declaratively bind to the view model. The view becomes a mix of XAML and C# (as WPF or Silverlight controls), the model represents the data available to the application, and the view model prepares the model in order to bind it to the view.

The most important aspect of WPF or Silverlight that makes MVVM a great pattern to use is the data binding infrastructure. By binding properties of a view to a ViewModel, you get loose coupling between the two and entirely remove the need for writing code in a ViewModel that directly updates a view. In a sense, Views and unit tests are just two different types of ViewModel consumers. Having a suite of tests for an application's ViewModels provides free and fast regression testing, which helps reduce the cost of maintaining an application over time. A good article about MVVM