Posting back here the results of a quick search in April 2008 after not finding any specific detail here on shuttles. Note there at least a couple of fixed-price, greet-and-drive services that give you a driver with a wally-board at arrivals, and an exclusive-use car to rival the service you would get in a taxi.
However, absolutely no representation at all made here about the quality / safety etc of the vehicles / drivers, but options include;
Super Shuttle A prominent, professional shuttle service, with operators nationwide. Sample quoted fares; $36 from airport to North Shore ($22 each for 2 pax, $17 each for 3), $25 to Auckland CBD ($16 each for 2 pax, $13 each for 3). You may or may not get the shuttle to yourself.
President Taxis Sample quoted fares; $65 from domestic terminal to North Shore, $60 to Auckland CBD. Fare good for 1 to 4 passengers. Claim to have only S class Mercs (no mention of their age). This is the company used by
The Spencer on Byron in Takapuna.
Kiwi Shuttle Fares listed on website; $35 from airport to North Shore in shared minibus ($21 each for 2 pax, $16 each for 3), $25 to Auckland CBD in shared minibus ($16 each for 2 pax, $13 each for 3). $55 to North Shore in an exclusive-use car (car make / model unknown), $45 to Auckland CBD.