Yesterday, a member at WebmasterWorld named Nitrous started a thread named Dumping the 200 filtered ads to see what happens! Basically, he removed all the sites he filtered in his Competitive Ad Filter list to see what type of impact it would have on his earnings over a 24 hour period. Well the test is almost over and the results are in as of midnight last night.
ECPM down by 25 percent. Earnings are 74 dollars... Instead of a hundred or so expected.
So it seems by this brief test, using the Adsense Competitive Ad Filter should increase your overall figures, if used properly.
Forum discussion at WebmasterWorld.