One of the nice things about both WPF and Silverlight is their ability to allow a designer to extensively alter the look and feel of a control without having to write code. A great blog to observe is Corrina Barber’s Ux Musings where she explains how to style some of the common controls that ship outside of the box with Silverlight 2 Beta 1.
Check out her blog here: http://blogs.msdn.com/corrinab/
Everything she shows, you can accomplish via XAML in Expression Blend 2.5, and our design surface will pick up and display the updates. We don’t support styling and templating via our UI (like we do for WPF)….yet for Silverlight 2! Expect that soon.