I've toured on both Islands, and loved it. I'd go back, well, according to Maori Legend I WILL be back to revisit one particular hill in 2015, but that's another thread.
Personally I didn't have any problems with drivers over there, except perhaps in Auckland. Overall I found New Zealand drivers much better behaved (on both islands) than what I'm used to dealing with everyday in this part of the world. There is definitely a higher volume of traffic on the North Island, but it's also easier to avoid the major highways on the North, while on the South, the major highways are often the only route between two places. I second the comment on the wind, but for the most part it seems to get stronger as you go further south, and from my experience, the strongest winds come from the west.
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I am clinically insane. I am proud of it.
That is all.