I had just arrived at work and was walking to the shop when one of the teamsters came out of the building looking shaken, and said "all Hell's breaking loose". I went inside where we have a TV in the break room and saw the first tower burning, and the reporters speculating on what happened, when the second plane hit.
All of us figured it was terrorists. Not much work got done for the first few hours, as we watched the story unfold.
I had just flown back from a training seminar the previous Saturday, so it felt a little extra eerie.