If you hold tickets on JetBlue, and your flight is canceled, your choices are as follows: accept a seat on the next available JetBlue flight, or get a refund to your credit card and make your own travel arrangements. (They do not have reciprocity arrangements with any other airline.)
We discovered this yesterday, when JetBlue cancelled our Sunday flight to RDU well after we had arrived at the airport... and the next available seat on a JetBlue flight was on Tuesday.
The "customer service" people at the airport were of absolutely no help. The 800 number to JetBlue wasn't being answered.
So we came back home and managed to claw our way onto a US Airways puddlejumper for Monday night. I may actually be strapped to the wing on this flight.
I think that's about it for JetBlue and me.