The execution was luck. The planning and conception was simply, brilliant.
Never underestimate a foe, friend. Give them credit where credit is due, then make sure that they cannot do anything like that.
DARPA, I believe, contracted moviemakers and script-writers to come up with the most fantastic methods of attacking the US, after 9/11. That is so DARPA could identify possible incoming attacks based on certain symptoms and activities. Now THAT was smart. I'm sure they did not poo-poo the idea of Al-Qaeda-set fires, but like Adam wrote, what can you do about that one?