I live in Palermo, married to Argie (we got married here in BsAs), and we see lots of same sex (male and female) couples besides us here, not just in Palermo, but also in other barrios. Just in our building there are a few, and we have friends who are same sex couples who live in other barrios and even outside the city. We do not advertise in any way that we are a couple and at the same time I have never denied to anyone anywhere when asked (I was in situations, for example in Iran, where socially I never confirmed nor denied, it was simply something nobody spoke or asked about, it was simply a given).
In the past I have lived and/or worked (while in previous relationships) in some places where same sex unions were legal (like Cape Town for example, Barcelona, or Bogota for that matter) and also in some of the most homophobic places on earth. I only say this in order to make a comparison and hence answer your question, so here we go:
Administratively speaking (renting a flat, going through the registro civil, etc), BA is light years ahead of Cape Town, based on my experience (same sex marriage is also legal in South Africa). In fact, not our landlords, not anyone at the registro civil, not anyone in any other place where we had to make it known that we are a same sex couple (like human resources for example) has blinked an eye when it came to any type of administrative chore in BA. In Barcelona I had equally good experience without any problems ever. I have also worked in Scandinavia and situation is similar - I never had any problems. I did also live in Poland and yes, even though I did not have any specific problems, you could sense the atmosphere was quite different once the landlady figured out that the blonde guy staying with me was not my brother.
One thing I cannot comment on is immigration here because I never tried to go with my DNI with him through the ARG citizen line - I imagine I could?
Now, on the other hand, I have noticed the following in BA: the word 'pareja' is in Spain used commonly by same or opposite sex couples. In fact, in Spain, at work, at immigration, etc, you can be asked in a casual conversation about your 'pareja' and it does not mean same sex partner. Here in BA,when people do ask me, they ask about my 'mujer', not 'pareja', assuming that I am married to a woman. In fact, during a job interview here in BA, when I used the word 'pareja', the person interviewing me followed up with a question if 'SHE' is from Argentina.
If we are talking about social life here in BA and if 'the ambiente' is truly LGBT friendly, my Argie and I are not perhaps a good example since our socializing is mostly done in the circle of few friends, both same and opposite sex couples or singles, hence someone else may give you a better answer.
Having said all of this, what I can share is that I have observed lots of gay couples here in BA which to an 'untrained' observed with preconceived notions of the gay stereotypes, masculinity, gender exp<b></b>ression, etc. may pass for heterosexual male friends. How can I tell that they are a couple (or casual sex buddies for that matter), as opposed to friends? You know the saying 'it takes one to know one'?
To summarize my response: based on my experience, I have never had any negative experiences here in BA, hence for me it is an LGBT friendly place, and I do see lots of same sex (male and female) couples.