i was a nielson viewer a couple of years back. if you dont have major electricity rates or are paranoid about privacy, take the option.
money-wise:
5 for the postcard reply
20 for interview
2 year term, @ ~$20/month with some signing bonus(dont remember how much maybe 120 - 200$?).
if they break any of your tvs they will pay to replace.
they install crappy cheap pc's to collect the data and send it back to the servers. the equipment in the tv monitors the audio and uses it to id the show. if they are on the same tech, you log into a small box on each tv when you watch.(they had like 3 pc boxes for 2 tvs and the 24/7 spike in electricty use negated some of the money reward)
semi annual interviews to update household stats.
at the tail end of it they offered a pc app to monitor your web watching.
if you want to affect what shows are made, be a responsible viewer. if you really want a show to survive, invite a bunch of teens and college students over to your house and have them in the room when the show is on. and buy pet food. they are really interested in people who buy pet food and wine.