Here's a quick refresher on the Google AdSense ad filtering tools:
Competitive Ad Filter: Let you 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.
Ad Review Center: Gives you additional control over the placement-targeted ads that may appear on your pages. Using the Ad Review Center, you can review specific ad groups and advertisers before they appear on your pages, and also block ads by type. You'll need to opt in to the Ad Review Center at the top of your Competitive Ad Filter page, and then you can begin reviewing ads.
In other AdSense related news; Google has released part 1 of three-part video series in english, that demonstrates top tips for increasing AdSense earnings.