Throttling Immediate TextBox Binding Behavior for Windows Phone

While developing Offline Web Browser for Windows Phone i had to build a small MVVM framework in order to keep the logic out of the views. One of the first thing i found missing was a way to force immediate propagation of text entered in TextBox control to the databound property of my ViewModel. By default, TextBox binding is triggered only when control loses focus, and this is kind of lame.