The idea behind the Ad Review Center is that when advertisers target your specific blog you now can see that they’re targeting it and can approve or ban and ad depending on whether you want it to appear on your site or not. This gives you more control over the ads that appear on your site.
Note – this is only for ads targeted to your site (ie general AdSense ads that are contextually placed on your site are not included).
Also keep in mind that when you remove an ad you could be decreasing the profitability of your site as it removes the ad from the ‘auction’ that happens between Advertisers to have their ad appear on your blog.
To find the Ad Review Center log into the ‘Setup’ area of AdSense, then click the ‘Competitive Ad Filter’ area and opt into the Ad Review Center program (it should be highlighted in a little green box).