I found out my USAir flight was cancelled by putting in a search via Travelocity for the same travel dates and departure/arrival sites. This was back in Sept. 2001. My first alert that something was amiss was when they first listed the flight as sold out. The following day it was listed as cancelled. I called USAir immediately and was rescheduled. Folks who booked the same flight through AAA were not notified until midweek. (We didn't know they were traveling the same flight until the woman told DH her woes with AAA.) If I didn't check, I don't think anyone would have called me. Travelocity didn't, when in years past, they would. The woman from USAir advised that Travelocity does not pass along the customer phone number for USAir to call. She suggested that I make sure the Air Carrier has my phone number in the future.
Do whatever you need to do to make sure your flight is still a go. Don't wait until you arrive at the airport...you might end up wasting a lot of time.
Good luck!
Sharon