I have this doubt. It is impossible to have a website with 100% US traffic. Is it one supposed to stop showing the ads to non-US visitors? Or does Yahoo discount this impressions and clicks? I also, remember I read somewhere that it was not just US traffic, but countries where English is the official language was allowed to be showed ads to. But I don't remember where I saw this. What do you think?
Sure - I redirect my international users to see adsense ads, and my US users to see YPN. You can use tools like openads or mySimpleAds to geotarget two sets of ads - one for US users to show YPN code and one for non-US users to show Adsense ads. That way you don't lose any revenue from non-US users.