Though I've never gone quite that far and boarded the plane, I have arrived early at an airport and sat in the gate area of what i believed to be my gate and only to find the gate had been reassigned another flight.

Lesson learned: if i get to an airport early, i get up and check the board every so often or else sit close to the GA instead of somewhere far off from him/her so i am more aware of activities such as gate changes.