I was at the Pasadena Hilton in California. I was a road warrior at the time, and had just flown into LAX the day before, to start a week-long gig at JPL. At that time I was a smoker. I used to wake up early and watch the news, while having a couple cigarettes. I turned on CNN and watched Paula Zahn, as I recall (whom I disliked) reporting on something and in the little video box above and behind her, I could see one of the towers on fire. I thought it was a fire.
Then I saw the video of the plane hitting, and I thought it was a terrorist attack immediately.
I knew this because I had downloaded and read a Rand report entitled "Homeland Security" a week or so previously (the report was several months old at that time) which suggested that Assymetrical Warfare was the wave of the future, said that this type of low-tech attack was exactly what we could expect, and defined how the department of "Homeland Security" should be created on the bones of FEMA and other organizations.
Yeah, it said all that. And no, I don't have it anymore. I've searched and searched for it, but it is gone. I remember it clearly - I even had printed it up and was reading it on the plane on 9/10.
Just as the second plane hit the tower (I saw that one live), my phone rang in my hotel room and it was my wife. She was terrified - her whole family basically works and / or lives in Manhattan. As it turned out, all her family was fine, thank G-d.
A coworker of mine had just finished up a gig in the towers the Friday before, and he was in the Marriott that got demolished in the smaller building (I forget which tower that was, not one of the big ones). All the people he had been working with were gone, lost.
Most of my coworkers were scattered all over, sleeping in high school gymnasiums, trying to rent cars to get home, etc. I was lucky, there was no place for me to go, so I stayed at the Hilton for two weeks until airline traffic was allowed again.
I kept doing the road warrior thing for a couple more years after that, but eventually the increasing security made my job miserable, going through airports twice a week every week, getting half my stuff stolen every couple months by TSA goons or airline people, and so on. I quit my job and got on with my life. Now I won't go near an airport if I can help it.
Sad days, sad times, and I remember it all very well. I'm so sorry for those who lose family and loved ones in the planes, the towers, and the Pentagon.