It was just recently that I learned that Google AdSense now allows an additional two more link units per web page (thus, total of three). I immediately implemented this new policy in my websites, Filipinowriter.com, PinoyFilm.com, WriteLit.com, and PinoyTechie.com, and there was an immediate impact on my Google AdSense earnings. Just today, for example, the link units accounts one-third of my AdSense earnings so far.

The best placement I have observed is in the header and top left areas.