I think since last year, and this thread sheds some light on the matter:
[webmasterworld.com...]
Shak
If I'm at Alexa and am just looking at the traffic info of a particular website, I am not entering any keywords. How do they determine when to show the ads?
It would be nice to know which sites my ad is being associated with. It doesn't look like you can find this out. The average cost per click is also higher than my regular clicks. I assume this is because I'm competing for placement with others who may be bidding on more expensive keywords. Hmmmm...
At the moment we have turned off content ads while we analyse those we have received and whether they return a commiserate higher ROI, and know more about how and when they are displayed. They did makeup a very small proportion of our adwords clicks, so its not a high priority other than turning them off..
And yes im pretty sure there is no way of checking (or controlling) what sites your "content" ads clicks come from (it's presently all or nothin'), though i think someone posted a way to extract the URL from the referring URL in your raw logs.