and on the sidenote, po is a used only by Tagalogs, a regional group of Filipinos residing mainly in Northern Philippines(esp. Manila) speaking Tagalog, which is constitutionally recognized as the official Language of the Philippines(naturally, only because the Capital city is in Northern part of this country). Whereas Hiligaynon is Filipino too, its more like the dialect spoken by Ilonggos of Central Philippines. We dont use "po", but use the word
salamat for thanks as well, so we can safely say "po" is a lingual form of respect to use regionalwise, especially when speaking the Official Filipino language(or Tagalog, in the truest sense).
sometimes, po can be used interjectively---like, "Po?!!!" and "Po?" which can mean "Really?!" and "Yes?" respectively.. One might hear Tagalogs saying "Opo/Oho"...which sensibly means affirmation (Yes)
Filipino as language and Filipinos as people is as complex as our geography, that we are sort of having identity and cultural problems