Was in 1st year Comp Eng, and left one of the labs to head down to the caf for something to eat. I walked past a big TV with everyone crowded around it, and saw a plane hit the first tower and though "holy shit what a terrible accident!"... then a few moments later was the video of the second plane...
Then I started panicking a bit; while I'm Canadian and live nowhere near NYC, my parents lived in Manhattan only a few blocks away from the WTC; they would in fact frequently go by/under/in the WTC around that time on their way to work. I remember spending the rest of the day very frequently trying to call them, but you just could not get through on the phone at all. It wasn't until a couple of days later I even heard anything from them at all to know they were ok.
Rarely have I ever felt that much anxiety about anything in my life; they sure had some stories to tell about the collapse, the panicked crowds, the cops, etc that they got to go through all first hand though. I think it took them a week to clear all the debris from the tower away from the building that they lived in so that tenants could actually go back inside to their homes.