>It is okay to use the 'tu' form instead of 'usted?' When I was in some countries in Central America that was 'taboo!' Also Argentina I think was the same.

In some circumstances, it is. As Esparta told you, it is fair using it between peers. This is, however, something that evolved with time. When I was a kid (some 500 years ago <s>) it wasn't usual to call "tu" someone that you didn't know personally (but there wasn't email, neither).

In Argentina (specifically around Buenos Aires), we don't use the term "tu", but "vos" instead, to call our friends, relatives, or kids. This is quite unique. Thre are very few places in Latinamerica, and some people at Palma de Canarias who use this form. It goes all the way back to an ancient form of the language used indeed as very formal. I really don't know why we keep using this instead of the pervasive "tu".

That has some related linguistic differences. Esparta would encourage you:
"¡Sigue practicando español!"

While I would tend to say:
"¡Seguí practicando castellano!"

(Keep practicing Spanish!)

8-)

See you,