Our brains are hard-wired to search for meaning, to help us understand the world. For the most part, the brain does pretty well, but often people see patterns where they don't exist. This happens in numerology, wherein people seek special significance in numbers.
July 2007 is unique in that it has both an especially lucky and an especially unlucky day, both within a week of each other. The first date, July 7, was full of lucky sevens, while the luck supposedly runs out this Friday the 13th.