On the whole, the idea of site targeting, where advertises can quickly advertise in AdSense on a particular site, is a nice idea. But reports come way of WebmasterWorld that scraper sites are abusing this feature. Where irrelevant advertisers are using this option, in effect dropping the eCPM for advertisers they target. But when publishers did something about it, either dropping out of the CPM option or removing the "advertise on this site" option, they saw large negative results. Ann reported that her "income fell about 550 dollars for November because of it" and fearlessrick reports that his "average click declined by about 40% and has stayed there."
Not sure what options they have or what they should do, but it is an interesting discussion.
Forum discussion at WebmasterWorld.