For those that are interested and purchase tickets to get to work, send their families on vacations, or happen to be depending on an accurate schedule, RULE 240 might be worth reviewing. According to the FAA, the rule is still valid.

RULE 240 states that an airline must deliver you to your destination within two hours of the originally scheduled fight time. If they cannot, they must put you on another carrier.

RULE 240 transfers apply only when the cancellation or delay is due to factors within the airline’s control: mechanical problems, lack of an airplane or crew, a schedule change, or such. It does not apply if the delay is due to a force majeure event: weather, a strike, closure of the airport, and other “acts of God.” The specific language differs from airline to airline, but the general terms are similar.

Nakazawa

This conversation seems to re-appear around the internet periodically. Usually some random journalist seems to 'rediscover' Rule 240 in its pre-deregulation form.
According to the FAQ section at the FAA ATCSCC's website (What's New -- Air Traffic Control System Command Center), the following is stated about this topic:

"Where can I find information on Rule 240?
The term "Rule 240" refers to a rule that existed before airline deregulation. There is no longer an actual Rule 240. The term, as it is now used, refers to each airline's "conditions of carriage" policy. You would need to contact the airlines to obtain this."