Hi, I've done the opposite to what you're thinking of doing...I'm a kiwi that moved to the US for the few years. So I know a bit about the differences / realities of moving to New Zealand. I'd say do it, our US friends that come to visit us here are blown away by our little country and some have come back several times!
There is a tax treaty between NZ and the US, so you won't be double taxed. You will still probably have to file a US tax return while you are overseas though. Cost of living I'd say is pretty high compared to the US. Depends on where you live in the US and NZ of course! I'd say after living in California, COL here is comparable to LA. Less expensive in the provinces, but job availability would be questionable. In the cities like Wellington, Auckland and Christchurch, rental costs are high, salaries are lower than what you'd get in the US. Food and drink are more expensive (but very delicious). We have a welfare state, so stuff your US employers pay for (benefits, health insurance), are covered by the government here, so taxes are higher.
You'd probably be able to find a job in your field of work, but you might want to check your prospects with local employers. Don't know how the visa thing would work - a working holiday visa, if one is available from the US to NZ, is a good idea.
www.trademe.co.nz is a good website for all things (kind of like Ebay, with real estate and jobs).
www.seek.co.nz is another job site. Cheers Notsospendi.
