For the OP:
I definitely recommend checking out the Buenos Aires network of Couchsurfing-- there are more Argentinians there organizing things than any other nationality. I've only started checking it out recently and there are ALWAYS things going on, and they seem like pretty cool people (bilingual, too). On Monday I think I'm going to a sunset chess meeting in Puerto Madero if you're interested, will be my first CS gathering!
As for my experiences with the word "gringo:"
- I am from the US. About 80% of my social and professional life here is with locals, and about 50% of that group is with locals who are from outside of BA, mostly the campo.
- In three years I have never once been called "gringa," not once, but one time someone did refer to me as "la gringa" to someone else, but in that moment he didn't even know I was from the US, so....
- If anyone calls me anything it's Yanqui, or believe it or not: "La Americana."
- The only time I can remember really hearing the word "gringo" is when I went to a polo breeding/training ranch in Córdoba province, several hours from the main city, and it was to refer to two tall, blonde brothers: "Los Gringos." I can't remember their family name, so I'm not sure if their origins were German, Italian or what have you, but they were definitely not from the US!
- As for that "green-go" thing, a couple weeks ago an Argentinean guy tried to sell me that story as true, but I just can't really buy it... A quick search on Wikipedia says, "The word was used in Spain - although the word is nowadays rarely heard there - long before it crossed the Atlantic to denote foreign, non-native Speakers of Spanish."