Do you live in a dual religion household?
I would imagine this would be very difficult to deal with when raising children. My guess is that you would let children celebrate both ways (lets say Jewish and Christian) and decide for themselves as they got older.
For families with one religious person and one not I would imagine this would be even more difficult. Unless the non religious parent doesn't care if the children go to church, I could see where this might lead to issues.
Are you a dual religion household?