I think that your accommodation can have a major impact on the way you experience a destination, and in the case of Mi Casa in BA, it couldn't have been more positive.
Unbelievably, the first thing I did when I arrived in Buenos Aires was to leave my money belt, with my passports, credit card, iPhone and cash in the back of the taxi from the airport. Ignacio not only spent hours on the phone trying to track it down for me (and, against all odds, actually succeeded), he even went and bought me ice-cream to cheer me up. That's how amazing he is.
The house itself is a fusion of authentic, traditional Argentinian architecture combined with Ignacio's own elegant, modern style. It's airy, cool, relaxed and the perfect retreat from the sometimes hectic streets of Buenos Aires. The neighborhood is quiet, but central, and you can easily catch a bus or Subte to anywhere in the city.
Ignacio also has the knack of collecting great guests - everyone else in the house while I was there was friendly, fun and interesting.
In short, I can't wait to stay there again, and I highly recommend you do too. But only if you're awesome :)