I liked the the input from homeinbuenosaires. She also sounds like a babe.
I think like many people have already said, there is racism in every country and in every culture. In some places it's more obvious, and in some places it's looked down upon, but there is a general tendency to trust "your kind" and to distrust "them". Not sure if does any good comparing the racism in one country to another.
I think anyone who watches television in Spanish can clearly see how whiteness is favored, and presented as more beautiful. Anyone whose watched Latin American soap operas (and has never been to whatever country produces that soap opera) would swear that the locals tend to be fair skinned, with colored eyes, fairly affluent etc. The reality is often far different. The television, and magazines favor light skin, and this transmits to the local thinking as well (whiter is righter, haha).
However, my personal theory is that racism now a days has a lot more to do with classism. It's more often than not that the poor are discriminated against regardless of their skin color, though they do tend to be darker. Given that all of Latin America had a population of dark skinned natives, with white skinned colonizers (who ended up being the ruling class) people associated fair skin with wealth and power. There has been a lot of integration here since those days, but on the whole people in Recoleta are lighter than those in Moreno, and those in Recoleta also tend to be wealthier. It's just the result of the history here.
Some darker skinned people have a chip on the shoulder about this. In fact, I know one brown skinned lady who is 10 times more racist against "negros" then anyone else I've met here. I think she feels she has to prove she is not part of "them". The poor can also discriminate against the rich or middle class. It's the same classic trend all over the world.
I remember when I was in school that some kids would get left out of certain things because they couldn't afford to fit in with the in crowd.
I am a little darker than most people in Capital and my accent is such that I often get mistaken for a Peruvian. I find that people instantly relax when they find out I'm not Peruvian. That's given me some insight into how people often view Peruvians. I've had people change their whole attitude towards me, including body language and posture, when they realize that little assumption wasn't true.
I don't often get mistaken for a westener, and so I've also had the opportunity to hear a lot of people complain to me about the US, in particular. I've heard people say very hateful things about the States, for example "I hate that country, it should be wiped off the map." I don't think this reflects the majority of people's thinking and I think they often do treat Westeners very well, but there is definitely some anti-Western sentiment lurking about as well. This is especially true in leftist circles. I think it's the similar kind of thinking that says "that country is what keeps us poor, and they need to go".
Anyhow, I think there is racism here, and it's sucks to be on the receiving end of it. Overall, though, I've been treated very well, and I have felt very little discrimination personally. Some people may have a racist attitude, but they'll often judge people individually (at least once they get to know them a bit).
I've had the odd ball comment here and there, but I understand that before I was exposed to different cultures and ways of thinking that I too had many prejudices. Much of it is just ignorance and lack of exposure.