The Earth Will Be Peopled by Entirely Another Generation

Yes, they cared about this a hundred years ago, too. From the New York Times, December 12, 1912:

For those who delight in that sort of amusement to-day is a day to celebrate by writing a great many letters and dating them, each and every one, 12–12–12. The sequence of the twelves makes positively a one-day stand and no more. Those who put off their writing after to-day will never again while they live have this opportunity! When again a person takes pen in hand to indite a letter with the figures 12-12-12 in the dateline, an entire century will have passed, and the earth will be peopled by quite entirely another generation. Last year there was 11-11-11, but, alas there never can be a 13-13-13, unless they change the calendar a great deal.

Found via the indispensable Twitter account, The Times Is On It.