Windows Phone System Tray obscures FrameRate counters
Here's a small tip for those of you who want to debug performance in a Windows Phone Silverlight app with the frame rate counters, but have the System Tray visible - hide it.
The counters currently show up behind the system tray (since technically the tray is a system overlay which is drawing over the surface available to your Silverlight app), so hiding the tray will show the counters.
Don't forget: to re-enable the system tray when you're done!