My family and I were in Washington DC for a week spanning the 4th of July. At least for this week, the crowds were quite small, hassle was minimal and, aside from the HOT HOT weather, we had a lovely week. Tourism is way down, but it shouldn't be. The only disappointing thing was that it is now practically impossible to see the White House (by see, I mean literally "to view" the White House), because all the roads around it are closed off.
Yes, we worried about terrorism, but obviously not enough to keep us from going. I found it quite moving to be in such a historic area at this time and place (we took various day trips out from the DC area). It was, paradoxically perhaps, quite uplifting. Yes, our country has its problems as many on this forum are quite adept at pointing out. But we have an illustrious past, heroism, intelligence and creativity to spare, and it was brought home quite eloquently last week.
Simple example: while taking the Metro into the district to go to the Air & Space Museum, I looked around at everyone else in our car. Whites, blacks, Hispanics, Asians, Arabs, professionals, families, young, old, etc., all sitting next to each other sharing the ride into DC. I wanted to say "Take THAT, Osama!"