I was in middle school, out running on the track when the first plane hit... I came back inside before the end of the period for some reason that I can't remember, and I heard one of the coaches on the phone talking about something happening in New York. The talk in the locker room was mostly about how it was probably some power outage, no big deal, but I was worried. At the time, I had three relatives living and working in NYC.
I went to my next period (US History, ironically) and sat down just in time to see the second tower fall live, not one of the reruns... It was like everything just stopped for me. I knew that my cousin would have been in that part of Manhattan at the time, and I freaked. I remember people being pulled out of school for the rest of the day, and the sub in study hall being an ass and not letting us watch the news.
I found out three days later that my cousin hadn't just been in Manhattan, but she was under the towers in the subway station when the planes hit. She not only got out, but helped a blind man get to safety as well. There were so many stories of people reaching out to strangers in the panic and helping each other... and I think those are the stories that tell of the true American spirit. Even in a city notorious for the selfish and antisocial tendencies of many of its citizens, people were able to pull together to get through the dark time. The same for the people who managed to bring down the plane in Pennsylvania. They knew that they weren't going to make it, but they had a chance to insure that no one else had to die, and they took it.
So much in our world today is about us versus them, and it shouldn't be. We're all human, though we come from different cultures and have different stories. It's a shame that this is all but forgotten outside of tragedy.