Hi how many sites have you filtered with your competitive site filter on your adsense panel ? i'm givins the first answer , i have filtered 150 sites
I have not used the competitive site filter yet. If my CPC goes down then I will look into it, but for right now I don't think that it would help my sites.
I just use it when some annoying site gets their ad on my site. Fortunately I haven't seen any recently. Either the targeting is getting better, or the market for my keywords has changed significantly since I started. I have roughly 20 URL's blocked.