Recently launched Silverlight 5 beta having nice features of XAML binding debugging. To Start with this, as a prerequisites makes sure you have latest version Silverlight Toolkit SDK with Visual Studio 2010 SP1 installed. Once you are done with the setup, first create a simple Silverlight 5 Application with which has some XAL Data Binding.
Now you can set the breakpoint for the data binding in XAML Code. Run the Application When a breakpoint is hit, you can use the Locals window to explore the state of binding .
To know more about details how the data binding debugging works and what needs to do for your MVVM based application , One way and Two Way Debugging Please Read a nice article By Kunal chowdhury
There are some additional enhancement introduced with Silverlight Data Binding. you can get complete info from http://msdn.microsoft.com/en-us/library/gg986857%28VS.96%29.aspx#xaml