Some interesting information ....
Firstly, I wanted to test the COST issue. On the internet, I randomly selected a return flight SYD/HNL .. out 1/2/07, back 10/2/07. Here are the results for the cheapest fares(incl taxes, but not food purchaes) available on the Airlines' sites:
QANTAS
Economy $1693
Business $9358
JESTSTAR
Economy $1267
Star Class $2547
So, obviously, for this specific example, Jetstar provides a cheaper option ... with at least a 99.9% chance of getting there safely. I'm sure you can find other examples that don't weigh up... but I haven't got the energy to look.
MORE INTERESTINGLY, guess which aircraft runs both Economy outbound flights? Yes, Jetstar A330. (The Economy return leg for QANTAS is on a flight through Nadi.)
EVEN MORE INTRESTINGLY, guess which aircraft runs BOTH Business class legs for QANTAS? Yes, Jetstar A330. So, for $9358 you get Jetstar Star Class seating. That would be a shock as you walked out of the Qantas Club ???