After having just got back from Australia after a 3 week hol I can tell you that the plane journey really does go on, and on, and on, and on. We had one stop off point in Hong Kong but one of the flights was still over 12 hours.
They turn the lights off for most of the journey to gently pursuade you to sleep but there's nothing worse than waking up hoping you are nearly there, turning on your tv and finding you only slept for an hour and still have 8 hours to go. That was really annoying.
What is weird that I got no jetlag going there but I was out of it for nearly 4 days after returning, so don't plan on doing anything energetic or work that need concentration, for at least a few days after coming back.
I assume immigration control in NZ is similar to Australia, so be prepared to go through all sorts of controls when you arrive there. Took us nearly an hour after stepping off plane, to finally leaving the airport.
Anyway, have a great time!
Boo!