Me and my wife just got back from a wonderful 10-day trip to Buenos Aires, which included a 2-day trek in Iguazu as well.
I am writing here because I feel the need to give a positive note to all these safety concerns regarding the amazing city of BsAs. I have to say that we were really impressed by the vibrant life and the friendly people wherever we went in the city.
Neither myself nor my wife ever felt threatened or even witnessed any sketchy things happening to other people, at any point of our trip. We were walking all over the city with a DSLR camera in our hands, taking pictures wherever we felt like doing so without being hassled or anything. That includes walking in crowded places like San Telmo on a Sunday market, or Florida street where we exchanged money without having any issues, or even quieter places like Recoletta on a Wednesday night.
Again, I don't want to encourage anyone to do anything foolish like walking around without precautions on a sketchy sidestreet at night, I just feel the need to write down my own positive experience because I've read enough of negative posts before actually going there myself. I think that if you excercise common sense, like you would do in any other big city anywhere in the world, there is nothing to be worried about.
Buenos Aires is a beautiful vibrant city, in terms of people and lifestyle reminded us a lot of Athens and Madrid with a hint of Parisian architecture. Go there and enjoy it, excercise common sense wherever you go and please do not let all these negative posts regarding safety freak you out, just have a great time!