I got one of those a few weeks ago. Filled it out dutifully and mailed it back just like the instructions said. :-D It was a lot more personal than the regular census ever gets, requesting precise info about income, utilities used and how much I pay for them, ethnicity, marital status, whether I was on public assistance, how -- and how far -- I traveled to work / school, etc. It took almost an hour to fill out for just Billy and I.
I didn't see anything in the paperwork about getting paid to complete it, haven't heard from anyone since and no one has come by the house.
Yea we never got any thing in the mail. From what I have read most people receive it this way.
If you believe what the government tells you, they use the additional special info to properly apply federal monies for schools, highway projects and the like. Personally, I thought it was fairly invasive.