Having a single sign-on is cool for you application. In this day an age, it is enough to try to remember even 10 of your passwords. Outlook/Exchange, LiveID, Facebook, etc… If I had to remember a password for every website and app I have, it would drive me crazy. Good thing that we have claims based identity. Now I just need to remember my LiveID of Facebook Sign on (Among others). Now if you are creating a WP7 application and want to take advantage of that, you can take advantage of a nuget package that takes the hard work out of it for you. My buddy Bruno Terkaly has created step by step instructions on how to add this to your windows phone application.