title: I need to know how long the user has been idle
body: <p>I'm currently using <code>LayoutUpdated</code> on the <code>RootVisual</code> member of the <code>Application</code> object, but that isn't catching absolutely everything (for instance, it doesn't catch a <code>Panorama</code> control switching between <code>PanoramaItems</code>, nor does it catch taps on the <code>ApplicationBar</code>).</p>
  
  <p>Is there some other way to query the OS to find out how long it has been since the last time the user interacted with the device?</p>