One of my teachers was Argentinian and she was somewhat difficult to understand, true. The toughest thing to get used to was she was insistent on using usted predominently instead of tu and she always said 'Joe' (a softer ch sound, not a really hard J) not 'yo' :o)

I've often wondered what the inner emotional reaction is, when someone is addressed with 'tu' instead of 'usted'.

Any time I ever used 'usted', the response was a friendly, 'no, no, por favor, tu, no usted'. I guess it's the equivalent of someone calling me 'Mr. Goff' and then me saying, 'no, it's Kevin'.

I guess maybe the reverse is somewhat like the reaction (more like correction) I once received, of, "it's Ms." ;)