I just saw an article about this talking about how they're using drones and whatnot and still can't find the guy. This raises an interesting point, I think.
I always thought DC sniper style attacks across the US would be much more easily planned, coordinated, conducted, and terrorizing than a single grand attack if someone wanted to attack us. If rather than going to Iraq to fight Jihad, everyone had just visited the US, bought a rifle, and went haywire, we'd have been curled up in the corners crying ourselves to sleep every night.
So, we all assume that we could never bring down the government due to modern technology (if the need ever arose) but this whole situation shows the impact that true terrorism has. You don't have to actually be anywhere or do anything, you just have to convince people that you MIGHT be somewhere and MIGHT do something if you are there. The country is so susceptible right now that it's quite terrifying in itself.