Did you ever want to get honest feedback from Google on the 'on-page' optimization of your Web pages? Well now you can! Since Google released Google AdSense, you can determine, on some level, if your on page optimization efforts are focused on the proper keywords.
So if you targeting the keyword "search engine optimization" you should see ads on that page pointing towards search engine optimization services. Simple concept.
As an administrator, DaveAtIFG. over at WebmasterWorld said, "What makes this is handy is that your ads will change within a few hours of making changes to your page. If the ads are better targeted, you're done! If not, try again and review your ads in a few hours. You can (and should!) confirm your click through ratio within 24 hours."