I flew today on JetBlue 504 FLL-EWR. Like all the other departing and arriving jetBlue flights that day from FLL (and EWR, and probably LGA and JFK because of the weather) was delayed. However, this was not weather related, but instead due to mechanical difficulties. The aircraft was N556JB, "Betty Blue". When we were next in line to rotate, the pilot made an announcement that one of the ducts in the #2 engine was overheated and they were bringing us back to the gate so it could be worked on. A short time later, we de-planed, and it was determined that service would have to be done, so when the next aircraft arrived (I believe from LGA), N534JB, "Badda Bing Badda Blue" our flight was switched to that ship, which I believe was supposed to be used on flight 506, the next flight to EWR. When I arrived at EWR, all of the jetBlue flights on the board were delayed, and I am sure this had something to do with it.
Other than the delays it was an excellent flight and the situation was handled very well