Brian Harry just announce about new Plugin for Visual Studio 2012 RC and Final that will enable support for Silverlight 4,5 in CodedUI Testing.
Using the Microsoft Visual Studio UI Test plugin for Silverlight, you can create Coded UI Tests or action recordings for Silverlight applications. Action recordings let you fast forward through steps in a manual test using Microsoft Test Manager. Coded UI Tests let you record actions, generate code and play back user interface tests using Microsoft Visual Studio.
This plugin supports Silverlight 4 & 5 applications hosted in Internet Explorer versions 8, 9 & 10. It requires Microsoft Visual Studio 2012 RC.