The 2010 Census form only has 10 questions. No matter what you might have heard to the contrary, all questions must be answered. If not, census workers will come to your door to complete the form via a face-to-face interview.
President Obama stresses the importance of participating in the census:
“Every 10 years, our Constitution requires the federal government to conduct a census. This helps determine your representation in Congress, as well as how federal funds are spent on things like schools and roads, and where businesses decide to put new stores and factories. So when you get your census form in mid-March, take about 10 minutes to answer 10 questions — remembering to include everyone in your household. Because we can't move forward until you mail it back.”
For more information about how the Census operates, see the Census blog.