I'm attaching a link describing the ACS.

http://www.census.gov/acs/www/

The Census bureau isn't trying to invade your privacy. These surveys and censuses are important. They help measure the economy and they help determine how monies are allocated and so on. I'll admit some of the surveys are a pain but the end results usually benefit the economy as a whole. They also go to great efforts to protect your personal information. Nothing ever personally identifies a person. If you don't feel comfortable answering some questions, don't. I've filled them out and nothing will happen. They are happy to get what they can. Good luck! :-)