Slashdot is a bad example. Back when it was owned in Ann Arbor, I kept ads on - to reward the site for giving me value.
Since the buyout by Dice, I now check the box to hide the ads. They are a large for profit company, they can live just fine without my ad hits. Oh, and most of the ads I do see on this site are for other Dice sites. I don't want to reward bad behavior.