You'd think a level headed guy like me who fears ONLY Grizzly Bears and Great White Sharks would dismiss the fear generated by the 13th day of the month falling on a Friday in any given month.
And you would be right. While I don't often challenge the dark forces of nature-- and I'm certain they exist, I don't give much weight to the impact of the event, but apparently there are a lot of people who do. From Wikipedia;
According to the Stress Management Center and Phobia Institute in Asheville, North Carolina, an estimated 17 to 21 million people in the United States are affected by a fear of this day making it the most feared day and date in history. Some people are so paralyzed by fear that they avoid their normal routines in doing business, taking flights or even getting out of bed. "It's been estimated that [US]$800 or $900 million is lost in business on this day". Despite this, representatives for both Delta Air Lines and Continental Airlines say that their airlines do not suffer from any noticeable drop in travel on those Fridays.
So tread lightly today my friends.