An individual may make his/her own Customs clearance of goods imported for personal use or business. All merchandise coming into the United States must clear Customs and is subject to a Customs duty unless specifically exempted by law. Clearance involves a number of steps: entry, inspection, appraisement, classification and liquidation.
Items imported for personal as well as commercial use are subject to duty if duty is required on that item.
The fact that in most cases, nothing happens, does not mean that there is no import duty in the USA. I am not a lawyer, this is not legal advice. But this is not hard, folks.
Ever come back into the US and fill out a Declaration Form? Depending on what you bought overseas, you may have to pay duty on it, right then and there. NAFTA applies, as the title says to NORTH AMERICA.
Any person who says there are no import duties for items coming into the USA is wrong. They may have never paid a duty - either because what they brought it was specifically exempted or because they just slipped through the cracks - but that does not mean duty is not due. Speeding is illegal - most get away with it. But you can't say that speeding is therefore legal.
At the link listed by someone up above, click on "U.S. Import Requirements (doc - 64 KB.)" and read that.
Duty has to be paid if there is a duty on that item. If the item is valued at over $2,000, Customs may seize it until duty is paid. That's where the $2,000 limit being discussed came from.
There is a monster list of what is dutiable and what the rate is listed on that page as "The Harmonized Tariff Schedule of the United States," but the link appears to be down at the moment. I have a copy of it at work, I had to use it to pay my duty on film (gee, I thought there was no duty) so I can look up camera stuff tomorrow if you like.
Best Regards,
Bill "Not a Lawyer, but Smarter Than One" Mattocks