I should add that if you're after a good NZ summer, typically late Feb/March is a good time to visit. School summer holidays are over and its much quieter. Conversely, if you're trying to find anyone to do any real work (other than a skeleton crew to hold the fort) from late Dec to early Feb you're usually out of luck. Early Autumn/Spring is also not too bad to visit. This year seems a little odder than usual in that Spring has been much much wetter than winter (certainly in Wellington anyway).