Some agents say it was cancelled for mechanical problems. And some say it was because the flight wasn't full enough.
Canceling a flight because it wasn't full enough is utterly bogus. The airline's incompetence at load management should not be my problem.
Of course, the rebooking message didn't have anything useful, like what time and what gate my new flight will leave at.
And UAL was too cheap to have a gate agent at the gate I arrived at.
So I called up UALs 800 number, and walked the menus to find my reservation. The first time through, when it was supposed to transfer me to an agent, it suddenly jumped back to the first menu, and the second time through, it kept cutting off it's own messages and misinterpreting and missing my responses. But finally I got to a human agent, who was very obviously a cheap outsourcing, with an almost inpenetrable accent.
My flight was to leave at 7pm-ish. Yay, so much time at the airport!
Then I saw a sign for where UAL has human agents at a given gate inside the airport. So I walked there, and there was, amazingly, no line! And a competent agent!
He found an open seat at a 5pm-ish flight, and booked me onto it, and printed my boarding pass.
So now I'm here at this gate. And the gate agent here is being deluged with people. Apparently a flight to Vegas got cancelled and then the pax rebooked onto a flight that leaves thru this gate, but without enough seats. And then the next flight out this gate is my flight to Philly, and there are a huge pile of people who were going to be on my original flight who are now here on standby.
I mess the "old days" when I could just call up Pat at Peak and say "fix it, please!" and it was done.
I have been remarkably lucky at one single point, finding that competent human agent at a desk without a line.