They change all the time. I saw something called PetMed and Ferretstore.com, but right now its for mortgages and realarcade, a game website.
I just ignore them- as I do on google And if they help finance the site I am fine. We all know that a contribution system wouldn't work probably. Content you have to pay for is a problem- although there are people on this site who would be happy to pay a little.