>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.
"Tu" is used to be more personal, I mean between developers (an any with the same status) is common to be more "tu" we call it "Tutearse" (I don't know the english translation), but when you reffer to someone with highest status like an Old Person, a Boss or Chief, you call it by "Usted".
It's an issue about be or not polite. At least in the region where I am in Mexico.