My girlfriend and I were watching Portlandia today and they asked this question to one of the characters and it got me curious as to where people where when you first heard about the plane crashes? It's interesting that most people can't recall what they did on their 18th birthday, but everyone seems to remember where they were when they first heard about the crashes.
I was in 4th grade at the time and I was meeting up with my neighbors to walk to elementary school. My neighbor came out of her house and asked if I had heard about the planes crashing into the Twin Towers (being a 4th grader, I had no idea what they were to begin with). It was cloudy that morning and my neighbor thought that all the clouds may have been caused by the smoke of the crash.