Hasn't happened yet, and I really doubt it ever will. They had their chance with the Smoketown Bandits, but since they were able to figure out who it was before they got within shoot-down distance, they were able to handle it cleanly, and their systems and procedures have been improved since.
Just remember that every incursion into this zone by one of us will be reported nationally (even internationally), and will be seen by the general public not as evidence of security lunacy, but of our incompetence, and another reason to ban "little airplanes" from the sky.
So please -- read and heed, and don't $%&* it up for the rest of us.