Here are some numbers on a test I did long ago 20k uniques per day entertainment site (9 months ago) with 25% international visitors. 60% of the clicks were from international peeps and 40% from the US. How did I know? Basically, I geotargeted the tracking. If the ip was international then I used a different ad code. Here's the logic. Say a German visitor gets to your site. Everything is in English including your YPN ad. If he sees a pic next to your ad he will click on it. If you ad is on the very top of your page and that's the first thing he sees, he will click on it. If you had an adsense ad, it would be properly geotargeted and will have a message in German. Also, some of the YPN ads apply only to the US...for example. Say a German guy who can read english comes across an ad that says "US Government Grants. Anyone Can Qualify". And this guy says, hey, that's great...the US is giving away grants!...and so he clicks on that.....I'm sure you get the picture