Mark Arteaga – fellow MVP just helped me with this,  thought I’d share.

Windows Phone 7 SilverLight supports persistent storage, which is a great way of saving settings betweens runs of your application.

However I couldn’t get it to work.

If you do this to create a persistant storage instance -

   private IsolatedStorageSettings userSettings =
IsolatedStorageSettings.ApplicationSettings;

To retrieve settings do the following -

string xx = userSettings[“SomeValue”].ToString();

Hiowever the bit that got me was how to save settings, you have todo this -

userSettings.Add("Hello", DateTime.Now.ToShortTimeString());
          userSettings.Save(); // <- This is the bit that got me

Hope this helps others