What I'd like to focus on is the origins of the polite second person pronouns, which, for me, always seemed a little bit unnatural. Did they always exist?
     To begin with, it seems appropriate to relate some basic of the second person pronoun, so that we know what to ask about it. Most persons are likely aware that Latin-based languages like Spanish and Portuguese use one pronoun for addressing family and close friends and another for addressing relative strangers. Most persons are probably also likely aware that in King James English, both the pronouns thou and you were used.

Language	Familiar	Formal
English	Thou	You
Spanish	Tu	Usted
Portuguese	Tu	Você
French	Tu	Vous

     What seems interesting about these different formal pronouns, is that they developed rather independently in very similar ways. All are descended/derived from second person plural forms. Originally, one didn't say "you", one said something similar, but more ancient, but ignoring that technicality, "you" was originally only used for talking with a group of persons, but then what happened is you met someone you didn't know and you felt kinda awkward, and the other person felt kinda awkward and in order to distance yourself from the person you were speaking with, you refered to that him/her as a group instead of as an individual. (Perhaps you knew somebody who was in some group with the new person.) It made the other person feel more comfortable too. Perhaps it makes you both feel like even though you don't know each other, you know each other's groups. (Even if you don't even know what kind of group you're refering to.)
     That seems to be pretty much what happened in all languages that use this kind of formalism. People just feel more comfortable talking with strangers or even, in an uncomfortable (or formal) setting, with friends, in an indirect fashion. As odd as that may sound, it's true and it even happens today. The loss of the second person plural has given rise to all sorts of words to fill the gap in our language.
     "You" has come to mean what "Thou" and "Thee" once meant and in order to distinguish between one person and his group, (Singular and plural) english speakers have invented a great many solutions, the most famous, though not the most widely used, of which is "y'all". (You+all) However such solutions don't really seems to solve the problem as "y'all" has come to be used as a singular in many cases in exactly the same way that "you" migrated to a singular.
     Is this phenomena also occuring in other languages currently?

     The French formal pronoun developed much as in English, except that French has preserved the distinction that "vous" is the plural and "tu" is the singular, whereas English speakers remain almost universally unaware that "you" is technically a plural form. In this way French also differs from Spanish and Portuguese which created separate 2^nd person pronouns to be used formally and ended up treating these 2^nd person pronouns as 3^rd person pronouns when conjugating verbs and such. Of course, this makes sense because Spanish and Portuguese use a 2^nd person posessive pronoun to treat the person one is talking to as a thing external to the conversation. ("Your mercy is", as opposed to "you are".)

Language	Formal Pronoun	Etymology
Portuguese	Você	<-Vossa Mercê ("Vossa"="Your" plural)
Spanish	Usted	<-Vusted <-Vuestra Merced ("Vuestra"="Your" plural)

Resources:
     Yall (Youse, Yuns) Should Read This