In a case of mistaken identity (of a place rather than a person) my United flight to Portland last night was delayed and had to re-connect the jetway and switch passengers.
As we were getting ready to push back, one of the passengers got up and talked to the flight attendant in the front of the plane. They talked, she talked to the pilot, they talked some more. All I could here was "I'm really sorry" coming from the passenger.
The jetway re-connected and the guy got off the plane (while another passenger, who had been denied boarding because the plane was oversold, got on -- lucky him).
Apparently, the departing passenger had booked the tickets, checked in, and boarded the plan without realizing that he hat ticketed himself to go to Portland, OR, rather than Portland ME. I would have thought that the 5 hour flight time would have given him a hint, but perhaps the fact that the 3 hour time difference made the apparent time difference (if you didn't pay attention to timezones) appear to be just 2 hours.
Anyway, luckily we hadn't gone far and he didn't have any checked baggage (nor, from what I could see, much carry-on luggage -- just a small laptop case). So after the quick switch we were on our way.