(1st) Senior year in college. Woke up, did some online browsing before class, saw something about a plane hit one of the towers (I think it was actually from ATOT I first found out). Walked by a construction site on the way to class, who had their radio going. Announcer said it was actually passenger jet, and then another jet had just hit the other tower (not one worker was doing anything, just standing and listening). Got to class, professor kicked us all out and suggested making sure everyone we knew was okay. Went to the student union, watched in a crowd as the first tower fell on TV. Walked home and watched the other tower fall with my roommates.
Was completely distracted in the one class that the professor refused to cancel that day (lecture attendance counted for some dumb reason). So was everyone else. More or less, everyone just stared blankly forward. I didn't see one person taking notes.
I remember several people freaked-the-fuck-out as they couldn't get ahold of loved ones in New York when that first tower fell.