The US Census of 1850 marked a real change for people researching family trees. This was the first US census that enumerated every member of the household and included the age, place of birth and occupation. By the 1880 US census, information about the birthplace of the parents was included.
Each census, thereafter, included some relevant additional information. I won't see the images of the 1940's census for another two years. I wonder if that census will give more information.
I filled out the 2010 Census form for my family. As a person who frequently looks at the US census images from 1790 to 1930 as well as those from other countries, I was really disappointed with the questions asked in the 2010 US Census.
Nothing was asked about the birthplace of my parents or whether I was a citizen or not. Nothing was asked about when I came to the US if I was not born here. Nothing was asked about my occupation or whether I was employed or not.
I suppose that the Census Administration wasn't thinking about how the information collected might help people in the future researching ancestors and relatives who lived in 2010.