Jacquie - I doubt traffic conditions have changed very much. Looking at some other riders comments I can only assume I have a high threshold of tolerance for traffic - perhaps as mentioned because I have ridden heavily trafficked city streets for many years.
On another visit (see my North of South journal) I rode SH1 from Picton to Christchurch despite dire warnings about traffic. I encountered no issues at all.
Common sense says you must stay alert and visible - perhaps wear hi-vis clothing (I didn't), and use daylight running lights front and rear (I did). And be prepared to pull off the road and even dismount if necessary to give heavy traffic room to pass. There are some long one-lane bridges that seem quite daunting but many have overtaking points along the way. Otherwise I would just take the lane. I've even had some motorists escort me across them.
I also observe how Murphy's Law applies to traffic:
1. If a vehicle approaches from ahead, another will almost certainly approach from behind and both will cross you at the same time.
2. If a vehicle approaches from behind, there is very likely another one (or more) following closely behind it.

Reading this 12 years after its posting, I'm hoping your comments on the roads and traffic are still valid. I, too, do most of my riding in/near an urban area so I'm always wondering about how bad the NZ roads really are.