I was on the way to my client at the time, heard the news break over a local morning radio show. Confusion as to the first plane into the tower (accident?), and utter horror at the second collision. I was fortunate enough to be working in town. The director at our firm that I worked with quite frequently was in the towers that morning, however. His tower was the first to get hit...his meeting was moved that morning...from a floor in the 90's, to a floor in the 60's. He made it out okay, but you can imagine the impact that had on his priorities (I think I'll call him today).
As for our project team, we then heard about the Pentagon being hit. All the news websites were overloaded, so we wheeled in a TV and saw the two towers fall. We all packed up our computers and headed home to our families for the day at that point.