There are some very good reasons to be extremely skeptical of the probing questions the census asks. First, let's look at what the Constitution says about the census:
Article I Section 2: 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.
It's pretty simple. The federal government counts the number of citizens every ten years to apportion congressional representation to each state. However, the census has come to be an extremely probing process, asking for your name, age, race, and relationship status, among other things. And that's just the short form. The long form, which goes to a randomly selected set of people, asks 53 questions: everything from your income, how old your house is, and even what you use to heat your home. What does that have to do with apportioning members of congress? Good question.
There is a lot of resistance to answering these questions, and with good reason. One site I found, called Don't Trust the Census, makes a pretty good case for not filling out the probing questions. They point to research showing that census data was used in 1943 by the FDR administration to round up and put Japanese-Americans in concentration camps. So much for the census promise that "responses are confidential."
The main reason the Census Bureau cites for filling out the questions is to make sure that we get our share of the federal welfare state's booty: "People who answer the census help their communities obtain federal and state funding and valuable information for planning schools, hospitals, roads, and more." Sure.
What to do? Well, federal law says that you can be fined $100 for not answering the census, but my research shows that the last people actually prosecuted for this were in 1973. The Census Bureau claims they've never prosecuted anyone for not filling out the form. I don't mind abiding by the constitution, so in 2000 I simply filled out the first question, asking how many people lived in my home, and I mailed it back. They sent one of their goons out to extract more from me, but I wasn't home, so they gave up. It was pretty simple.
Keep in mind that only 67% of the people responded to the 2000 census and no one was prosecuted for not responding.
Some additional links that popped up around the 2000 census: