We were recently bumped off a flight and I have to think that it was without cause. We were booked w/ confirmed seates from Costa Rica to BWI thru Miami. Although our flight out of Costa Rica left late, our flight out of Miami was also detained so that the plane was still there when we arrived at the Miami gate. We had been confirmed w seats all the way thru, yet they would not let us board the Miani to BWI plane b/c they had already reassigned us a flight (unbeknownst to us) the next day thru Boston. Although AA did give us a voucher for a hotel room that night and rebooked us on the next flight out the next morning, I still think that this was an injustice since we had confirmed seats and we were there 15 minutes before the plane even left. I would appreciate any advice you can offer as to how I write my letter of complaint to the airlines.

Since you were coming off an international flight it was difficult for the gate agent to determine if you could make the flight. Immigration and customs can be a PITA sometimes. S/he had to make a call. It went against you this time but that's the way it goes sometimes. Don't forget, the GA's main responsibility is to make sure the flight leaves on time. How would you feel if you were 1 of the 150 on board the plane and you were told the plane is being held up for a connecting passenger? Then ATC held the flight for another hour or 2 because the departure slot was lost? I'm sure you would be posting here asking why does that happen?

AA gave you a hotel and meals. Part of flying.

Write a well worded complaint and you may receive some miles, but don't expect more than that.

I'm still waiting for an answer from British Airways when they messed up in early March. I actually told them I didn't expect anything, just an explanation and apology. Go figure!

Part of travels......

The AA agent probably gave your seats to a STANDBY couple, once they determned you probably will not make it to the flight.

Ditto AAFF
You weren't bumped, you missed a connection because your flight out of Costa Rica was late. If that delay was for a "compensable" reason - i.e., something not under the airline's control - then you may be entitled to compensation above and beyond the hotel voucher.
And the anticipatory rebooking was actually a nice thing to do - the alternative would be wait until you arrived, tell you you missed your flight and have to stand in line to find alternate booking.

A confirmed seat is only confirmed if you show up during the required time before the flight is scheduled to leave - scheduled is the key word here. The required time prior to flight has gotten a little longer in recent years - to ensure on-time statistics are kept, for security, and because planes are so full - there is usually someone else on standby who would just love "your" seat.