For poeple who are flying on AA:

AA will not reschedule/reroute you until they have official confirmation that they flight is cancelled, which at the earliest is 12 hours before the flight, even if it is blatantly OBVIOUS (my particular flight has not flown the past four days!).

Something you can do (beside hitting the redial button to AA) is to make sure that your phone number is on file with AA so that they may call you to inform you that your flight is delayed.