The Day of New Blood

For a group of people built completely from minds that knew the world before, remember it, and long for it, the thought of bringing new life into it can be a frightening prospect. There is, however, a certain... freeing effect that it brings, showing that one is as only tied to a long-gone past as they let themselves be.
The Day of New Blood is a celebration of that feeling. As we know, the internals of the Ms operate just as they would if they were an Organic's. They can conceive, carry, and birth children like any other form of life. When this happens, it brings communities of Ms together. Often inspiring an "it takes a town" type mentality.
The biology lesson is beside the point, I suppose but related to the Day.
Every year, the M population of colonies, tribes, and city levels come together in what can be a rather varied day of celebration. The proceedings can be anything from the simple and personal dances and feasts of frontier towns, to the esoteric and somewhat alienating rituals of upper floor Ms and the more insular cults out there. Though I suppose those are one and the same, often enough. The connecting string between all of them is the celebration and adoration of the children born that year. The New Gen, if you will.
Gifts are often exchanged, much like the old world concept of a baby shower, if a dozen different families were doing it at the same time, in the same place. Announcements of upcoming births and even marriage proposals occur frequently during the festivities.
The day also serves as a celebration of the New Gen children who have survived to adulthood. An impressive task, wherever you are, and many towns have more specific traditions and rituals for those now young adults.
Every form of celebration is acceptable (though we don't talk about what the wetland tribes of Zhongguo do on this normally auspicious day) and the only thing that brings it down are the dangers of this world, which can show up at any time.
And Organics.
It's become such a common occurrence, Organics with even a bit of authority trying to put a stop to the festivities for widely arbitrary reasons, are simply ignored in most places. Those more experienced power brokers know, and often teach those below them, the lesson that their predecessors learned the hard way. 
Sometimes people need their traditions, and they get very angry when you try to cut them away.