I have had a lot of positives, some the same as mentioned above - The rounding down of payments when they don't have change is a regular thing...
Living out of "tourist land", the smiles and delight that people give me when I talk to them in my bad Spanish, and they then want to spend the rest of the morning talking to me, offering help, and asking why I am here.
The email from the head of the department at the University I am studying Spansih at (who I only met once), congratulating me on my impending grandfatherhood.
Being amazed at the great beer that you can find here (Obviously not Quilmes or the regular Commercial beers) - The Artesenal Ones, the Brew Pubs, This was truly amazing here, and so unexpected.
One night coming home from San Telmo in a remis, with the driver playing a CD of his favourite songs from english language bands of the 70's, I was singing along (maybe I had partaken of some of those beers mentioned above), and when we reached home, he ejected the CD and gave it to me to enjoy the rest of the tracks at home - And refusing the tip I tried to give him, both for the journey and the CD...
There are so many - I love this place