For instance, IIRC the census asked for my and my wife's country of birth and nationality, but later on when filling in the info for our children, it asked for the nationality of the both parents again. Simple logic checking back through the data should have shown that our (the parent's) information was already supplied, and this information for our children could be pre-filled or skipped and auto filled in the database.
Just a few small things that would have made the filling out of the forms a lot smoother, faster, and less complicated for lay people who were already nervous about doing the data entry.