I find it instructive to dig deep into my pay-per-click campaigns in order to get the most information abou the "ROI" or return on investment from my adword spend. I used to spend a considerable amount of time digging through my http refferer logs and using some third-party solutions to help my tracking. Now, google has added the function directly into their service:
View site-by-site metrics, optimize your performance on content pages, and gain greater transparency into your campaign with the Placement Performance Report.
The Placement Performance Report is a new report type in the AdWords Report Center that provides site-by-site performance metrics - including clicks, impressions, cost and conversion data - for domains or URLs where your ads have appeared on the Google Content Network.
In other words, you can track the return on your investment from specific websites. This is an excellent way to eliminate sites that have fraudulant clicks or are simply not paying off. You may have an overall conversion of 3% for a campaign (that could be number of sign-ups for your newsletter or number of sales etc.) but then you find that a particular site has generated 500 clicks but no sales nor subscriptions.
What do you do? Google will not only allow you to identify those URLS but also eliminate them from your adwords campaigns - saving you money and increasing your ROI. To generate these reports, log into your Adwords account and go to "Reports" - "Placement Performance."