This is very good for web sites that have ASP.NET Authentication (or plan to have) and have Silverlight apps.
Brad Abrams, from his blog:
"Here is what I plan to show:
1. Login\Logout 2. Save personalization settings 3. Enable custom UI based on a user's role (for example, manager or employee) 4. A custom log-in control to make the UI a bit cleaner "
Source code available on the above post.