Been on JetStar a few times in the past year without any problems and generally happy with their service until they changed my flight without notifying us.
Slight disappointment with the service but I must emphasize it has only happened once. With the change of flight which could not accomodate my time, it did incur quite a bit of losses. (Had to get a refund which was a bit of a trouble, have the insurance cancelled on our expense, and top up for a last minute rate which was not remunerated for)
Since then I have not taken JetStar but I would probably do so soon because their service on flights have been quite pleasant all these while.