Haha one of my friends' rellies said "Jetstar flights are too bumpy". I lol'd. Obviously they order the wrong weather to fly in.
I travelled to and from Nagoya with Jetstar in December/early January, and the flight was great. I paid for food and entertainment beforehand but I could have lived without it. The new airbuses are awesome, as comfy as any regular airline. Great service too.
The only problem is that the flights were late, to and from Japan, as a result of planes arriving late and a small radio problem. My friend travelled separately to us and her flight from Cairns was cancelled so she had to go to Osaka and transfer and was 4 hours late.
I'm sure this happens periodically with most airlines, though. Australia is a really safe country to fly in/from.