The number "wu er ling" (520 in Chinese) sounds approximately like "wo ai ni" (I love you in Chinese)! Hmmm maybe not that alike but because of this similarity, Chinese couples use 520 as an acronym or abbreviation for I love you.
If you never knew, well now you know ;)
whendidyoujointwitter.com. The result will be shown like this.
祝 有 情 人 终 成 眷 属 =]