Just saw this pop up in eHOw.
Had a quick look at Sydney and its for 4th Feb to 20th March and 6th May to 19th June (presumably these are for departure dates). These are on sale till 2nd December.
It may be for other cities and other times but I just thought I'd let everyone know if they want to scrabble around on the Jetstar site.
As a review, I liked their business class - it had foot rests which Virgin didn't have, but doesn't have flat beds like Garuda, but I'm sure you'd make do!
Hope this helps someone.