I sometimes fly C transatlantic and domestic F within USA on the same ticket. It is getting almost impossible to change a ticket last minute since all seats are taken by Y passengers. Once my F flight was cancelled, they put me on the flight right after in Y "sorry, we cannot upgrade you on that flight" to which I answered "I paid F!". In several occasions I felt that all staffs in USA consider F fliers as just upgraded passengers... But well, at least american airlines have proper F seats, unlike AF "premium affaires" on the new non reclinable seats within Europe!