We use Adwords to generate leads, but long ago selected the option to prevent any of the ads from being served on the 'affiliate' sites. For our business we found that to be an absolute waste of money.

We DO generate lots of revenue from people buying our services when they search for them directly on Google, but never a dime from people reading blogs, etc vaguely related to our material. In fact by placing our Ads in the affiliate network we felt like we were more subject to click-fraud than we were on just the main google search site.