I got the long form in 2000, too. I didn't return it. Someone came to the house and I told them the questions were too intrusive and they should leave my property. They sent another person out, who threatened me with a fine. I got wiser and told them I lost the form and if they would just leave another on the doorstep, I would send it in. I never did and they never contacted me again. By the way, they told me they already had the names of those living in our home, supplied without my knowledge by the local postmaster (extremely rural area).
I got the long form and didn't send it in too. When they came to my house to ask about it, I looked them in the eye, and said, "Two." When she asked what I meant by that, I said, "The Constitution requires me to tell you 'two' and nothing more. That's how many people live here."