I'm confused after reading this article: http://traveltips.usatoday.com/much-money-can-bring-united-states-100169.html
In the first paragraph, it states: "You may bring up to $10,000 in currency, coin and certain monetary instruments without reporting it to customs."
But later on, it states: "You must report all coins, including gold coins, and currency from the United States and other countries.", which would seem to indicate that you must report any cash amount, even below $10,000.
By reporting, I'm talking about the form you have to fill for customs.