I have family in Chicago, but it's safe to say that I wouldn't really feel any safer there.
I think it's important to set up a "buddy system" of sorts just in case something goes down and the internet is unaccessible to a friend in the affected area.
In terms of investments, real estate should remain a safe bet although any property owned in the area of an attack would be rendered worthless. For those who own outside of that area however, the value should skyrocket.
If I had the money, I would buy land in a rural, less populated area where the likelyhood of attack would be slim to none. That way, should I lose everything where I am now, I still have a place to go and live, even if it's in a trailer home.
I think real estate is always good, but I suppose a castastrophic event, say a bomb went off in DC and destroyed a major amount of our government, could so seriously disrupt our concepts of the value of money, that even there confusion could reign. I think these kind of implications are beyond me to figure out.
Interesting that David Hackworth, FWIW, and I don't know what it's worth, considered living in Manhattan, but decided against, it because he thought it was too vulnerable to terrorism.