-History-
Being my Spanish as it is, I read the Spanish Wikipedia Article on the subject located here, and I got the gist but I didn't feel confident enough to attempt explaining it in this post. I read the English, and it was a little bit better but the article was still chronologically confusing. Finally I read the Hebrew version and it was much more simplified and clearer than the other two. Here is the excerpt with my translation:
השימוש בסימן ההפוך בתחילת המשפט החל במאה ה-18. בשנת 1754 האקדמיה המלכותית הספרדית פרסמה את המהדורה השנייה של (כללי הכתיב בשפה הספרדית), ובו קבעה כי בנוסף לסימן בסופו של המשפט יש לשים סימן הפוך בתחילתו. קבלת הסימן על ידי הציבור הייתה איטית, ובספרים שהוצאו לאור בסוף המאה ה-19 לעתים לא נעשה שימוש בסימנים אלה. כיום הוספת סימנים הפוכים
בתחילת המשפט נחשבת לכלל מחייב, והשמטתם מהווה שגיאת כתיב.
The use of an inverted punctuation point at the beginning of a sentence began in the 18th century. In the year 1754 The Spanish Royal Academy printed the second edition of the Ortografía which established that in addition to the final punctuation point an initial punctuation point should be added to the beginning. The symbol was accepted by the community slowly, and in books which were printed even in the 19th Century at times did not utilize these symbols. As of today the use of the inverted symbols is considered compulsory, with its exclusion being considered a typographical error.<Source: http://he.wikipedia.org/wiki/%D7%A1%D7%99%D7%9E%D7%9F_%D7%94%D7%A4%D7%95%D7%9A>
In summary, despite the initial call for inverted punctuation in 1754, it wasn't until the mid 1800's that it actually became common practice!
-Usage-
In general from what I've learned and read, the inverted punctuation goes at the beginning of the question - not necessarily the beginning of the sentence. Example: Pablo, ¿me quieres? and ¿Me quieres, Pablo?. Also, something that seems to be in debate between different places I've looked is the use of different marks at the sentence's beginning and ending, i.e. ¡Cómo lo hace? From the gist of it, it seems as though using both symbols, i.e. ¿¡Cómo lo hace!? in symmetrical order is the most preferred way to go.
The English Wikipedia article goes on to mention that today in chat rooms where the initial-inverted punctuation would prove tedious, their use is commonly either ignored or replaced by their duplication at the sentence's end, i.e. Por qué dices eso??, much to the chagrin of teachers, seeing the practice popping up in school settings.
¡Hasta Pronto!