They want only the most basic of demographic data from me (is this really me, do I live here, who else lives here, how many TVs do I have). I'm sure they cross match it all from the more standard marketing demographic databases, tho.
Apparently, they are aware of the existence of PVR boxes like my ReplayTV, and the tech who will later come to install the box will know what to do to make it do "the right thing" without messing up my setup. Of course, I wonder what "the right thing" is, as I almost never watch "live tv", which will mess up all their calculations. I suppose they could just count everything that it records for me, but I routinely do things like throw away already-seens, watch a few favorites over and over, and record random things "on trial", and then throw them away after 5 minutes of viewing.
Their box sits silently behind my system, with no user interface, and it "phones home" via landline POTS to a 800 number every night at 3am.
What do I get out of it? Other than helping to increase the ratings of my favorite shows, they give me money (USD75.00) AND they pay half my video cable bill.