Sorry to be the bearer of bad news guys, but it looks like Mario Kart Wii has been pushed back to April 30 in NZ, though this date is just an estimate from Gameplanet. It's quite possible the game could be delayed for longer.
Here's the relevant info from the news post on GP's site:
The local Nintendo distributors have informed us that the New Zealand release of Mario Kart on Wii has been delayed.
The distributors have not given a reason for the delay, nor are they able to provide a new ETA at this stage. Rest assured that as soon as we have an updated NZ release date we will update our web site and everyone who has pre-ordered.
What's worse than a delay? No reason being provided for said delay.
As for the April 30 date? It's from an email GP sent out to its customers.
Mario Kart (Wii) NZ release delayed [Gameplanet Store, thanks everyone!]