I have flown with Jetstar many times and didn't know this.
My son has decided to take his girlfriend to Melbourne next month for the valentines break. (Don't know where he gets that from...certainly not his father! ).
Anyway, he was looking at flights and the different times.
There were early morning flight prices on Jetstar but they changed to a more expensive price ($80 each) later in the morning. He saw a price on Tiger airlines that was much cheaper and was within an hour of the Jetstar flight so he gave Jetstar a call. They matched the price and gave an extra 10% off. Instead of paying the online price of $160 for two tickets he paid $80 and there wasn't any booking fees or add ons.
I will make use of this in the future and thought that I would let other people know as it will apply to the other Jetstar routes. It really is worth checking to see if anyone else has a cheaper flight even if you might not want to fly with the other carrier.