Just had the displeasure of taking a trip on the 787 to Bali last week and have to say it will definitely be the last mid/long haul flight I ever consider on these.
Economy cabin is effectively the same domestic slimline A320 seat crammed into 3-3-3 high density configuration.
Was seated in row 10 which as a bulkhead has decent knee and leg room but this did little to offset the discomfort of the reduced width and elbow room - being seated effectively IN the window.
Little or no padding to the seat means you should consider taking pillows for your b@tt & back!
Arrival was accompanied by hip, elbow and back pain.
In addition the cabin is very understaffed for their service plan - our pre-ordered meals came out first but then all call bells for ignored for hours whilst the crew struggled to handle the buy on board service for the rest of the cabin - at 1 point there were 8 rows illuminated with calls in the front mini cabin alone. In the end we dumped our trays in the galley after getting sick of crew darting passed avoiding looking at us.
If Jetstar really think they can make long haul work as an LCC they'll need to rethink their approach, can't see how even the most cost-conscious punters would consider a second go in these pain-buses.
If you're considering travel to Bali I would be recommended Virgin or Tiger's 737s over the Nightmare-Liner (or Garuda)