Scince April 2009 Google announced the release of adsense interest based ads that is serving ads relative to visitor interest rather than website content.. scine then I did not notice any effect ot increase in ctr or even as a visitor ads were still absolutly relative to website content today I saw a php scripts ad on an environmental blog ! I think I am the one was targeted as a webmaster also I noticed some increase in ctr so I think interest based ads are just starting to take effect