It’s a mistake many Adsense rookies make: the site’s keyword-optimised and attracting exactly the ads they want, but the clicks are low. So they up their Adwords budget and drive lots of traffic to the site, but the revenue per click is always less than the cost per click Adwords is charging.
It’s caused by using [...]

Refining your AdSense advertising program to cater to the needs of the most Web traffic is both an art and a science. The growth of social networking and blogging networks is encouraging people to click on advertising that is specific to their needs and behavior, and can benefit them in the long run. Contextual advertising [...]