Supposedly I just earned this privilege. I clicked on the link and it took me to a page that lists a whole bunch of other privileges but not "see reduced ads". It's not like this website is brimming with ads to begin with (another browser tab I have open has ads for Norwegian Cruise Lines, University of Nebraska and Viagra, and that's just without scrolling down).
According to the privileges page, I have "vote down" privilege and I'm close to earning "view close votes" privilege. I don't know what the latter is, but there's a page that explains it and will tell me if it really is what I think it is. Is there such a page for "see reduced ads"?