Hola Pinky,
My answer to that would be a definite yes. The formal and informal uses can be very important in their specific contexts in Spain, and particular in written Spanish; any classes or tests that I have done have emphasised it, and you can lose marks. Equally you can gain them by picking up on the less obvious ones - like talking to a police officer (or asking someone for help) where formal gets you real kudos especially in a live situation i.e. not only that you are treating them with respect, but that you can speak Spanish!
I travel to parts of Spain where the formal is rarely used, but I am often surprised how often it still comes up in shops and even some restaurants. Maybe it is because I am getting older and probably look it, but that actually makes the point. I think it's a good rule to learn, and to use the formal if in doubt. If the person answers you with the informal it is a good way to learn.
Saludos. John
