This is a good article from Gadling about what to do when your flight is cancelled. I see people complaining a lot when their flights are cancelled or delayed, and I want to yell at them, THE ABSOLUTE LAST THING YOU SHOULD DO IS GET IN LINE WITH EVERYBODY ELSE. Of course you’ll be annoyed then. Waiting in line with hundreds of others in the same situation will get you nowhere (worst case scenario) or on a flight three days later (best case scenario).
The last time I had a super delayed flight (AUS-ORD-YYZ, delayed for seven or eight hours), I called United and was immediately rebooked on another airline, on a flight leaving within the hour. It probably helped that I have elite status with United (which has its own phone numbers) BUT I did get home that night, unlike everyone else who waited around and ended up getting stranded overnight in Chicago.
The moral of this story is: do not wait around! Be proactive and you’ll get home a lot faster. (And I won’t have to yell at you.)