During the 'rush hour' at Houston's Hobby Airport, my flight was delayed due to a mechanical problem. Since they needed the gate for another flight, the aircraft was backed away from the gate while the maintenance crew worked on it. We were then told the new gate number, which was some distance away. Everyone moved to the new gate, only to find that a third gate had been designated for us. After some further shuffling, everyone got on board, and as we were settling in, the flight attendant made the standard announcement,'We apologize for the inconvenience of this last-minute gate change. This flight is going to Washington, D.C. If your destination is not Washington, D.C., then you should 'deplane' at this time.'A very confused-looking and red-faced pilot emerged from the cockpit, carrying his bags. 'Sorry,' he said, 'wrong plane.'