OK, I've imported an iBook from the US to NZ.
First off, the warranty. Apple's portable products have an international warranty. Desktops don't, unless you buy the AppleCare Protection Plan.
As for tax, yes, I was taxed for my iBook. I received a bill from Airborne Express for the tax, I paid them, and they paid the Government. The tax took me by surprise - I didn't know that tax was payable on imports. It turns out that under NZ law, if you import something worth over NZ$450, you have to pay tax on it. I guess other countries have a similar system.
And before you ask, the reseller I bought it from no longer sells outside the US 🙁