See our blog post on this. Many others I've spoken with have also found these same exact sites in their top "click" list. These sites are pure "junk" sites that are staging clicks, they have nothing to do with our industry yet result in wasting 80% of our budget. The "Placement Report" is a new report, it totally exposes these "scam" sites. It could be that 100 million is being wasted on this in the Content Network. I've written to Google and asked them to remove such sites from the Content Network. The result would be way less income for Google, so how can they honestly police this problem?
The Blog
http://www.entityspaces.net/blog/2007/07/10/TheGoogleContentNetworkWhoIsClickingOnYourAds.aspx
Many others have now "discovered" these same sites thanks to this new report. These same sites are eating up thier budget for zero return. I just hope the "Placement Reports" aren't pulled by Google, if they are we will go with other advertisers.