This is the last Friday the 13th until next June, and the next one after that will be February, 2009 - a year which has thee of them.
Fidel Castro and Margaret Thatcher were both born on a Friday the 13th, as were Mary-Kate and Ashley Olsen. Coincidence? I think not. :-)
Looking at the usual online sources, it seems the number 13 has a very brief history as being unlucky, references don't go back much more than 100 years. However, Friday as an unlucky day has been found in print as early as the 1500's, and might even be traced back to the earliest Bibles, being the day before God rested. He must have been pretty wiped out by that first Friday.
My work buddy Oleg says he thinks we get Friday the 13th from a historical event "The Night of the Long Knives", in the middle ages when the Church and its thugs arrested a bunch of Knights Templar, who were later executed. Lots of sources mention this as a possibility. But I doubt that this one minor political coup which was SOP for popes of that era, would have even registered with the masses, much less imprint itself into popular superstition. My vote is for turn of the (20th) century media hype, reinforced by Hollywood.