If you have logged into your Google Adsense account lately, you have probably noticed a new message just under the Earnings Overview section. Its called an Optimization Report, and will read something like this:
Here is your optimization report for the month of April. After an automatic review of your sites, we think you might be able to improve your monetization using the following tips...
My own report said "You may be filtering ads that monetize well on your site." Many others have reported the same (source). In addition to sharing the account-specific tip, Google offers a help file related to their suggestion. In my case, a link to Keep your filter list small.
I wont be following this advice, though. The URL's that I have listed in my Competitive Ad Filter are those that were "site targeting" my websites. For more on that, see: Adsense - Getting Paid Per Impression.
Still, the Optimization Report is an interesting new feature and I look forward to seeing the tips they offer in coming months.