from an adwords forum poster re content network site
I turned it off for all of them when I started gettign ppounded by junk clickers on one particular campaign. It was just too much trouble to keep track of for the low conversions I was getting in the last several months. Most of the clicks were coming from junk sites that were only vaguely related.
There's that term -- junk sites.
I can't wait for G to introduce program/s or advertiser feature/s that will reward sites with good content and punish the junk sites. G's rebate incentive to adwords advertisers when they choose to participate in the content network is a sure sign that G is recognizing advertisers' hesitance to participate in the program. Now we need G to make more commitments to improving the program rather than just rewards.