I always suggest reading up on the contract of carriage. Heres a link to the US CofC. Below I copy and pasted the part of the CofC that should answer your questions.

IX. DELAYED AND CANCELED FLIGHTS
US Airways’ Responsibility for Schedules and Operations
US Airways undertakes to use its best efforts to transport the customer and baggage with reasonable dispatch. Times shown in timetables or elsewhere are not guaranteed and form no part of the terms of transportation. US Airways may substitute alternate carriers or aircraft and may alter or omit stopping places shown on the ticket in case of necessity. Schedules are subject to change without notice. US Airways is not responsible or liable for making connections, or for failing to operate any flight according to schedule, or for changing the schedule of any flight.

Notification
In the event of a flight delay, cancellation or diversion, US Airways will provide the most current information available to customers in the airport or onboard an aircraft in a timely manner. Flight information may also be obtained through the US Airways web site (usairways.com) and the US Airways toll free flight information number (1-800-94 FLIFO).

Extended Onboard Ground Delays
US Airways defines an extended onboard ground delay as being two hours or more. Customers will be advised prior to boarding if an extended onboard ground delay is anticipated. When an extended onboard ground delay occurs, the flight crew will communicate the status of the flight in a timely manner and advise if cellular phones or other electronic devices may be used. Customers will not be denied access to functioning lavatories or water. Exception: A small number of US Airways Express aircraft are not
equipped with a lavatory. The extended onboard ground delay situation will be assessed at regular intervals, and decisions will be escalated through operations management to coordinate returning the aircraft to the gate in order to minimize customer discomfort. Length of flying time will be taken into consideration when making these decisions. US Airways management at each airport has local plans which outline their procedures to handle emergencies and other unusual situations. These situations can include, but are not limited to, customer medical emergencies and severe weather conditions.
updated 02/01/06

Rebooking
When a ticketed customer holding confirmed reservations on a flight will be delayed because of a schedule irregularity (whether a missed connection, flight cancellation, omission of a scheduled stop, substitution of equipment or a different class of service or schedule change), US Airways will rebook the
customer on its next available flight to the customer’s ticketed destination without additional charge. If US Airways is unable to provide onward transportation, US Airways may attempt to rebook the customer
on the next available flight of another airline with which US Airways has an agreement allowing the acceptance of each other’s tickets.
Alternate Transportation If US Airways is not able to reroute customers on its flights or other airlines’ flights, US Airways may offer the customer ground transportation to the destination. If the customer does not accept the ground
transportation offered, US Airways will refund the value of the remaining flight coupons to the stopover or destination.

Amenities/Services for Delayed Customers
When a ticketed customer holds a confirmed reservation on a flight, US Airways may assume limited expenses incurred as a result of a flight cancellation or schedule irregularity resulting in a delay exceeding four hours, as outlined below. US Airways may also provide special amenities and services
which, in US Airways’ judgment, are required by certain customers such as unaccompanied children, customers requiring special assistance, and customers with medical conditions, in order to maintain the safety, health and welfare of such customers. Amenities will not be made available to a customer on any US Airways flight which is delayed or canceled in the metropolitan area where the customer resides or at the customer’s destination. When a flight is canceled or delayed by two hours or more, customers at connecting points in their itineraries will be provided upon request with a prepaid telephone card which can be used on a local
public telephone, or access to a US Airways telephone. US Airways will provide a food voucher to customers whose flights have been canceled or delayed for three hours or more during normal meal times, when the delay is not due to Air Traffic Control, weather, or other circumstances beyond US Airways’ control. The food voucher may be used at a restaurant in the
airport or a hotel restaurant for customers who are also accommodated overnight. The value of the food voucher will vary according to whether it is for breakfast, lunch or dinner. In the event of a delay or cancellation, overnight accommodations will be arranged by US Airways at their
expense for customers at connecting points whose flights are delayed or canceled because of circumstances within US Airways’ control for whom no alternate transportation is available. Overnight accommodations will not be provided for customers whose flights are delayed or canceled due to
circumstances beyond US Airways’ control such as Air Traffic Control or weather. Overnight accommodations include a hotel and transportation to and from the hotel selected by US Airways. Food vouchers will be provided if the delay or cancellation causes the customer to miss dinner and/or
breakfast. A prepaid telephone card or access to a US Airways telephone will also be provided. In the unusual event that alternate transportation or overnight accommodations cannot be provided, US Airways will endeavor to provide for customers’ comfort by making sure food is available and
arranging for customers’ trips to resume as soon as possible. With respect to amenities made available by US Airways, including ground transportation and hotel accommodations, the vendor providing such service is not an agent, servant, employee, or in any manner under contract with US Airways to provide such goods and services. US Airways disclaims all liability for
any acts or omissions of the vendor, its agents, servants, and employees resulting in personal injury ordeath, or loss of or damage to property.