9000 was used as the first entry in the xkcd thread My number is bigger!. It is also the number of possible four-digit postal codes, which don't start with the digit 0. 9000 was also referenced to an episode of Dragon Ball Z in which Vegeta and Nappa are very suprised at Goku's suprise boost of attack power, creating one of the longest known internet memes "It's over 9000!!!"