Check this out from the AdSense blog:
When we notice a spike in readers who are interested in a specific topic, we like to address it as soon as we can. There’s been some interest in filtering ads from publisher pages, so here’s a quick refresher on the filtering tools we offer:
Competitive Ad Filter
You can restrict contextually-targeted and placement-targeted ads from appearing on your pages by adding the URL of each ad to your Competitive Ad Filter. After logging in to your account, click the AdSense Setup tab and visit the ‘Competitive Ad Filter’ page. You can also find full instructions and tips for entering in specific URLs in our Help Center. To determine the URL of an ad, try the AdSense Preview Tool or follow these steps. Please keep in mind that it may take several hours for the filter to take effect.
Look, I run a network of high end publishers, and many of them use Google and other remnant networks to backfill ad inventory. So I see this too. And I can give you exactly one reason why this came up. For those of you too lazy to click the link, Google came out against Proposition 8 a while back, and I applaud them for doing so. And the spike they are referring to? Most likely (I have not confirmed this) it’s because the Yes on Prop 8 folks are aggressively spending on Google right now, and a ton of publishers are seeing Yes on 8 ads on their site, and they don’t want to allow those ads.
For the record, I am openly against this proposition. If that means another group of readers (yeah, I am for Obama too) stop reading me because they think my views don’t fit theirs, well, sorry to see you go, folks. Most likely, most of you left me already given my views on the presidential electon. Somehow, I sense, in a decade or two, this will all seem like a pretty stupid debate.