Jeff Prosise discusses one of the exciting new features in the Silverlight 4 beta, namely a pair of properties added to the ButtonBase and Hyperlink classes named Command and CommandParameter.
These properties represent the first real support in Silverlight for commanding, which is primarily beneficial to to Model-View-ViewModel (MVVM) applications. MVVM has long been popular among WPF developers and is rapidly gaining popularity with Silverlight developers. And now, thanks to commanding, Silverlight comes a little closer to supporting pure MVVM implementations without help from auxiliary frameworks such as Prism.