when should formal language be used?
As a native english speaker learning spanish, I was wondering if someone could explain when the formal Usted(es) is supposed to be used? Is it always used when speaking to someone older than i am? Strangers in the street? Servers at a restaurant, or sales people? How about people in my family who I am very familiar with? Is it just a form of extra respect, or is it a serious infraction if i don't use it when i'm supposed to?
Usage varies from place to place, but in general, use tú only when speaking to family members, friends, close aquaintances, or children. Even though in some places, it is acceptable to use tú upon meeting someone of similar status, if you aren't sure, always resort to usted. If someone starts speaking to you using tú and the person is not an authority figure or someone older than you, it's generally safe to also use tú with them. And yeah, it can seem presumptuous or rude/impolite if you don't use usted when you're supposed to.
In Latin America, ustedes is used when speaking to more than one person, regardless of formality. In Spain, you should use vosotros in cases where you would be comfortable addressing everyone in the group with tú.
I lived in Spain for six months this past year, and I rarely heard the usted form. Even high school teachers were referred to by their students in the tú.
I used the usted form when talking to concierges, waitresses, sales staff, etc., but I heard Spaniards using the tú often in those situations as well.
Some people addressed their in-laws in usted, others in tú.
So, I would say play it by ear. Listen to what the people around you are using, and follow suit. It's really a situational thing and also depends on country. Spain is very relaxed about using usted.