I actually made a US flight that I originally missed for exactly this reason. I got to the gate just in time to see the plane heading down the alley. As I was about to rebook, the gate agent got a call on the radio... the flight was on it's way back! And I was going to get a seat up front!

The flight returned to the gate and the scene must have looked like a prisoner exchange at checkpoint charlie... as I was walking down the jetway, another PAX was on her way up looking pale as a sheet.

I sat down in what must have been her seat, we pushed back, and off we went. As we were climbing away from BOS, I pulled the paper out of the seatback pocket and noted the headline -- USAir flight goes off the runway at LGA. She must have read that and lost it... rather than fly with a distressed PAX, they returned to the gate to get rid of her.

Lucky me... I got to my meeting on time