Okay, this is digging up an old thread, but found this video that is quite convincing. http://www.adsensevideos.com/
It is interesting that you can't access the DOM in the source IFrame because it is located on a different site (google's). But they got around it by checking to see the URL in the status bar with the ad is clicked. A clever way to find out which individual ad was clicked on. But it doesn't look like they have integrated YPN yet. Maybe that is why it is called AdSense Tracker and not YPN tracker. Some of the cool features is that it will give you which IPs have clicked which is something Google doesn't tell you in their reports. But I have noticed that sometimes the results don't add up to what Google says.