I took part in the Nielsen survey for a while, years ago.
It worked exactly as this article described: You’re sent some crisp bills up front, in return for keeping track of everything you watch. You must write everything down on a type of chart. At the time, I was a notorious channel surfer, but, because I was so detailed, Nielsen invited me to do more surveys. I think they sent me $10 at one point.
Wow! I think I only got paid $1. Life is so unfair.