Thanks, Bic...I had read that somewhere but couldn't remember where....
Also from the FAQ:
How do I know the form I received isn't counterfeit?
Any request for census information from the Census Bureau will be clearly identified as coming from the U.S. Census Bureau and as OFFICIAL BUSINESS of the United States. Before your household receives a mailed form, a phone call or a visit from the Census Bureau, you will be given a few days’ notice with a letter from the Census Bureau Director.
I filled out and returned the form but a census taker visited my home anyway.
Quality checks are used to assure our procedures are working and that our staff is doing the job they were assigned to do. These checks require that some households be visited more than once. Additionally, if you returned your form late, your response might not be logged before a census taker is sent out.
Why does the census taker visit my home more than once?
Census takers visit local homes up to three times to record resident information for 2010 Census. The census taker leaves a door hanger, featuring a phone number, each time, if the residents they're trying to reach aren't home. Residents can then call the number to schedule the visit. In addition, quality checks to ensure that census procedures are working and census staff is doing their job will require that some households be visited more than once.