Seattlepi.com says that if you want to have a baby born on 11/11/11, you need to fuck on Friday. From the "article":
This should go without saying, but I’ll say it anyway: If you have your heart set on having an 11/11/11 baby for some reason, this is your only chance. The next time the calendar aligns like this will be Nov. 11, 2111.
Yup, that goes without saying.