I flew about 10 days after 9/11, actually going to BOS where there was talk of an ongoing threat there.
I had a very eerie feeling going to the airport that day, but once I got on a plane and we took off, I started to relax since my mind recognized the familiar travel routine.
When we landed in ATL for the connection, I saw it as empty as I had ever remember it. I don't think DL had resumed its full schedule, but luckily none of my flights was cancelled.