Ben,
I did experience the customs process there. I bought the bass from a club member in the US and had it shipped down to Hamilton. There was a bit of customs paperwork and some declarations- I didn't declare it a gift.... I have my permanent residence, but really didn't feel like drawing the ire of customs or NZIS if they called my bluff.
Yeah- my suggestion is call up customs, let them know which carrier it's coming in on and then ask them if you can fill out paperwork in advance. It'll make the process go quicker.
Toby