As far as I remember, Visual Studio (both 2008 and 2010) used to have an option to break either on thrown exceptions or on unhandled exceptions. Now when I bring up the Exce
This seems to indicate it can occur if you don't have "Enable Just My Code (Managed Only)" enabled.
Edit: just tried it here (VS 2008) and I can verify that disabling that option will cause the User-Unhandled column to disappear. You can find the option here: Tools -> Options -> Debugging -> General