The overworked YOU

Ever notice the paucity of 2nd person pronouns?  Unlike 1st and 3rd person pronouns, with the exception of  the possessive form (your/yours), we have one word to do it all.  Singular, plural, subject, object -- it's all the same to  youEnglish once had 12 forms for the pronoun of address, including a dual number.  Yes, there was a pronoun to say the two of you - how cool was that?  If I'd been around back then, I'd have voted to keep that form.

I'll thou thy teeth down thy throat!

Thee and thou were used at that time only to servants and inferiors; and no other Quaker peculiarity seems to have given so much offense as this one. William Penn describes the indignation with which people would turn on a Quaker and exclaim:

Thou me, thou my dog! If thou thou'st me, I'll thou thy teeth down thy throat!

To which the Quaker would reply by asking:

Why, then, dost thou always address God in thy prayers by thee and thou?
---The True William Penn by George Sydney Fisher
During the 1,000 or so years that English transformed from a language whose meaning is derived primarily from word order rather than inflectional case endings, other fun stuff was happening to youIn Early Modern English, there was still a distinction between the singular and plural form.  Singular:  thou, thee, and thine.  Plural: you, yours.  But we had no distinctive form for social class or level of formality.  We find evidence of English speakers playing around with this distinction, most likely due to the influence of the Norman conquest.  For reasons probably related to rhetorical styles used in the pulpit, the plural you was appropriated as the term for showing formality or respect.  With the beginning of the rise of the middle class, the line started to blur between who was worthy of being shown respect.  So, just as a caution against insult, you became the standard choice.  The Quakers refused to adopt you, believing it had originated from vanity.  They insisted on using the familiar thou to address everyone, which by this time had become an insult in some settings. Having come to be associated with those rebellious Quakers, thou fell totally out of favor.

The end result, thanks to that short dance with T/V factors English was left with one form of the 2nd person pronoun to do all the work. And ever since, it seems, English speakers have been searching for that missing 2nd person pronoun, presumably a plural form when in fact it is the singular form which has been lost along the way. In fact, you has retained its plural grammatical heritage: You are in my parking spot, for example. 
 So great is this need for a distinction between a singular and plural you, at least seven non-standard forms are in use today:  y'all, you guys, yous, youse, youse guys, you-uns, and yis.  And so odd is this lack of distinction in the world of languages, we can even find evidence of  the non-standard y'all being purposefully incorporated into a lesson for teaching Spanish to English speakers:
To avoid confusion between you (singular) and you (plural), we will employ the non-standard English usage "you-all" to indicate you (plural). This will be very beneficial to y'all, particularly at the beginning of your studies.
Complicating matters even more: It wouldn't be totally unheard of to enter an establishment in, say, Texas - completely alone -  and be greeted with a hearty Howdy, y'all.  Having nothing to do with a singular/plural distinction, this use of y'all reflects an attempt at friendliness and familiarity harkening back to the old distinction between the familiar and formal address long ago abandoned.  And, at this point I must confess that, even though I am not a Southerner, I have actually heard myself utter this bewildering arrangement of words:  How are all of y'all doing today?