The interview consists of three phases:
1. Aptitude test. Multiple choice, 28 questions dealing with math and clerical skills. The Census Bureau has a practice test that you can download to prep for the real thing. Pretty easy.
2. Mock Interview: You make believe you are a census field representative, asking some typical questions and writing down the answers. I believe that this is just to see if you are capable of reading aloud in a coherent, intelligible manner.
3. Structured interview. The actual job interview. After the interviewer reads your resume and application, he gives you a score based on the bureau's requirements for the job. He then asks you a series of scripted questions.
I worked as a Census Enumerator during the 2000 and 2010 decennial census's, so I felt I understood the skill set they were looking for. Census workers get a lot of push back from uncooperative respondents, and the job requires a strong ego, persistence, persuasiveness and closing ability. If you've ever been successful in sales you should be able to handle it. However, many cannot and the Census Bureau has a high turnover of their field personnel.
Overall I thought I did well. Unfortunately for me and other job seekers, the Census Bureau's budget was recently slashed by 25%, and Congress is likely to cut it more before the year is out. That's likely to put a big dent in their hiring plans.