This will hopefully be my last post here. I just want to make something clear, the whole thing is about the USE of the word American for US citizens. Not about the NOT USE of it, so there is a situation (is obvious, about that).

I'm not surprise a chilean will use "americano", they are US lovers so...

Anyway, as you can see I will cite some writings by your fellows Americans. Not just the name of an Archeological work from some University or what happened when in the hotel lobby. I will not even mention my own opinion, so take your time, read, learn and see that -at least- the use of "American" is not competly accurate and ambiguous.

" 'America' is used very generally both by writers and public speakers,
when they only intend the territory of the United States... It may have first came into
use as being much shorter to say 'Americans', than citizens of the United States"
-from Gazette of the United States, 16 Feb. 1791.-

"Every once in a while someone comes along who is perturberd
about Americans calling themselves Americans, feeling that we have no right
to use this term exclusively, that citizens of all nations os the American continent
are Americans."
-letter to editor, Christian Science Monitor, 1 Agu 1967-

"It is becoming presumtuous and inaccurate to refer to North Americans as 'Americans', specially in the context of defending or upsetting Central Americans, South Americans and Latin Americans"
-William Safire, NY Times Magazine, 3 June 1984-

"Names for United States citizens. International use.

International speakers of English refer to people from the United States as "Americans", while equivalents of "American" are used in many other languages.

French, German, Dutch, Italian, Japanese, Filipino, Chinese, Hebrew, Arabic, and Russian speakers use translations of American , to refer to U.S. citizens. Spanish and the Brazilian dialects of the Portuguese, use terms derived from Estados Unidos, the translation of "United States" – estadounidense and estadunidense, respectively.

In European Portuguese the term americano is used to describe US citizens or things. Although the term estadunidense is growing in usage, in Brazil americano is still said to describe U.S. citizens. These languages, especially Portuguese in both its European and Brazilian variants, also use translations of North American: norteamericano and norte-americano.

The same linguistic ambiguity that occurs in English when using the term "American" occurs in the other European languages; to compensate for this, French (predominantly Quebec French) and Italian speakers may refer to U.S. citizens as États-unien and statunitense respectively, though this is less common. German speakers may distinguish between "American" and "US-American" (German: Amerikaner and US-Amerikaner).

This confusion is also present in Portuguese, as people from the United States may alternatively be referred to as americanos in that language. However, in Spanish, americano chiefly refers to all people from north and south America, and using it in the United States sense, may be considered offensive to Spanish speakers; the Diccionario Panhispánico de Dudas de la Real Academia Española recommends instead "estadounidense."
-Names for United States citizens, Wikipedia-

Check this:
http://en.wikipedia.org/wiki/American_%28word%29

And... if is as clear as you say: Why is so easy to find so many articles about this subject? I didn't find any about if argentino is right or wrong.

Arturo

PS: Is a Cougar an American animal or should I say "this feline is both Southamerican and Northamerican"??

Well... I came to answer to Anwulf, but German already did my work.

I was going to say more or less the same.

However, I woud like to add:
1) http://en.wikipedia.org/wiki/Continent#Number_of_continents

2) I agree with the fact that an University got that "Americas" in its name. But you won't find that expression in day-life, news, newspapers. You can use it in some more... elegant or in a literary style of writing.

3) "Looks like they know that they live in South America." Surely we know where we live. If some people from Poland or Hungary know they live in eastern Europe do not mean there is a second European continent. I'm from the west region of my country, but is still one country.

4) I`m Argentinian as well, from Mendoza. Most people I know don't thnk the use of "americano" by US citizens is fair. I agree with German in this point: People you met was been polite.

4) Someone or something natural to the Americas, as you call it (without specify if is from North or South) isn't American?

Hay algo que no se ha mencionado: En español no utilizamos la palabra "americas" para referirnos al continente americano, se utiliza -simplemente- América.

Es sólo UNA masa de tierra, no tres. Asia es mucho más grande aún y no veo que se utilice las "Asias".

Creo que allí reside la diferencia en la interpretación de "americano". Just because in english people mean "american" to those from ONE america not the americaS, a concept that -as said- doesn't exist in spanish.