I've switched 95% of my flying to DJ and couldn't be happier. The main reason is that Qantas abandoned me. I travel a lot (gold on DJ - nearly double gold last year and will qualify again 2/3 of the way through this year) but about half my travel is MEL-NTL and Qantas have abandoned the route to Jetstar.
Ironically, on the route i fly the most DJ is the premium carrier. With DJ i get FF points, i get FF perks and i'm not treated like cattle. I can turn up 20 mins before my flight and still get on it. I get those benefits anywhere on the network and not just the "premium carrier" ports. With jetstar it's a nightmare trying to fly, you almost always earn no points, and they work their planes so hard that i've had many delays over 4 hours. Can honesly say that i've never been delayed more than hour or two with DJ and fly them ten times as much.
If you're like me flying QF just doesn't make sense - despite the fact the other half of my travel is between capitals and probably 10% of it would be business class (P/E on DJ) i can't justify splitting my spend/ points/ status across two carriers.
That's the danger for Qantas. More JQ means less loyalty. On the upside, DJ are improving their product. I now have Gold status with Delta and Virgin Atlantic - not yet a rival to QF but enough to get me to Europe and the states where i tend to go once a year, i can earn and burn on a reasonably wide range of airlines, etc.
My prediction is that i won't be the last to switch away from Qantas as they abandon more and more routes to JQ. DJ are improving their product and QF are diluting theirs - the "air bondi" announcements and cough are noticably fewer and far between. We'll see what happens, but Qantas can't cut forever without consequences.
777.