[UPDATE BELOW] NOT a good day to be flying on American Airlines (not that such a day ever really exists). The company is experiencing system-wide delays due to a nationwide problem with its computer systems, and has grounded ALL flights. The problem is that American has been unable to access its reservations system, called Sabre, which means boarding passes can't be printed, among many other important things. An estimated 100,000 travelers have been stranded at airports with only Twitter for comfort:

The latest reports say that American won't be able to resume flight operations until 5 p.m. EST. We'll update if more information becomes available.

UPDATE 4:45 p.m.: At 4:30 p.m., American Airlines announced, "Our systems have been fully restored, however we expect continued flight delays and cancellations throughout the remainder of the day... It is important to note we see no evidence that today’s technical outage is related to the tragic events in Boston." Read the full announcement here as you wait another five hours for your flight to depart.