It's also the feast day of Saint Wolfgang of Regensburg. A Facebook friend of mine pointed that out. Does he not have a cool name and so right for October 31st? Read about St. Wolfgang on Wikipedia.
He mentioned that Pope Gregory III instituted All Saints Day (the day Halloween is the eve of) four hundred years after the Celts became Christian. So, it is not, as is popularly thought, a rewriting of the pagan festival of Samhain. In fact Samhain was a lunar festival and not celebrated on October 31st. They didn't even have a concept of October 31st because they didn't use that sort of calendar.
Anyhoo, dig up the podcast and give it a listen.
BTW, for all you Catholics, All Saints Day (Nov. 1st) is a Holy Day of Obligation. So get your candy-filled selves to Mass tomorrow. :)