The ones here in Uruguay and especially Argentina are mostly concerned about illegally entering or withdrawing cash (US Dollars mostly).

You have to declare cash above a certain amount, and I believe excess cash can be confiscated.

There are also other questions (for example: if you're bringing animal products - we had very damaging outbreaks of foot and mouth disease, the mad cow scare, etc)

That's exactly what is on the customs forms going into the US, too. Of course, that doesn't fit into the conspiracy theories.

The I-94 form asks such questions as "have you ever been or are you now involved in espionage or sabotage; or in terrorist activities; or genocide; or between 1933 and 1945 were involved, in any way, in persecutions associated with Nazi Germany or its allies", "have you... procured or attempted to procure a visa or entry into the U.S. by fraud or misrepresentation?", and "are you seeking entry to engage in criminal activities?"

http://www.immihelp.com/visas/i-94w.html

Wrong form. The customs form is 6059B.

http://www.cbp.gov/xp/cgov/travel/vacation/sample_declaratio...

Yes, I know. I'm fairly confident it's the form tedunangst referred to, and to travellers, the distinction is mostly academic, since they're both handed in at customs.

That's not a customs form, to clarify.