Living in the Mountain Time Zone and typically working 9-6, I got out of bed after the first plane hit. Turned on my computer before the TV (shocker I know) and saw people online talking about something going on in New York. I turned on the TV just in time to see the second plane hit live. I was riveted to the TV and got to work late. The black cloud had descended on the office and very little work got done that day.
I still remember where I was when the Challenger blew up. I vaguely remember Reagan and Lennon being shot. But nothing had the impact that 9/11 did. Hopefully nothing else will in the future.