The purpose of the Census, as stated in the U.S. Constitution, was to simply count heads in order to apportion seats in the House of Representatives (and collect taxes from the States under the original revenue plan).
Representatives and direct Taxes shall be apportioned among the several States
which may be included within this Union, according to their respective Numbers,
which shall be determined by adding to the whole Number of free Persons,
including those bound to Service for a Term of Years, and excluding Indians not
taxed, three fifths of all other Persons. The actual Enumeration shall be made
within three Years after the first Meeting of the Congress of the United States,
and within every subsequent Term of ten Years, in such Manner as they shall by
Law direct. The Number of Representatives shall not exceed one for every thirty
Thousand, but each State shall have at Least one Representative
The rest of the information they gather is mainly to guide elected officials and bureaucrats in devising ways to redistribute wealth and create new schemes to divide Americans into various grievance-based groups. My race is none of their business. How many televisions I own is none of their business. Hopefully, 2010 will bring a widespread movement of Americans who reject Leviathan's intrusion into their lives.
On another point, did you notice that the Constitution called for one Representative for every 30,000 persons? Today, each House member represents about 700,000 people. Is it any wonder they are out of touch party hacks who don't give a whit about the Constitution or their constituents?