Why are people so enthralled with today's date? What's so special about 9/9/09? Heather whipps explains over at LiveScience, in which she blames Pythagoras:

Though usually discredited as bogus, numerologists do have a famous predecessor to look to. Pythagoras, the Greek mathematician and father of the famous theorem, is also credited with popularizing numerology in ancient times.

"Pythagoras most of all seems to have honored and advanced the study concerned with numbers, having taken it away from the use of merchants and likening all things to numbers," wrote Aristoxenus, an ancient Greek historian, in the 4th century B.C.

As part of his obsession with numbers both mathematically and divine, and like many mathematicians before and since, Pythagoras noted that nine in particular had many unique properties.

Link | See also Buzzfeed's Happy 9.9.9 Day!