A DigitalPoint Forums posting reveals how a member who used heatmaps increased his AdSense earnings after he discovered where people would click most frequently on his site.
A number of tools that provide HeatMaps are discussed, including:
Additionally, a link is provided to the AdSense Help Center page that answers the most ideal ad placement locations are.
Discussion continues at DigitalPoint.

Comments:
Cher
04/17/2007 05:56 pm
I think every technique should be within the guidelines. Indeed its a good tip to increase the earnings.
Oscar R
04/17/2007 07:00 pm
Am I the first who notices that the free option, ClickHeat, adds a link to their website in the noscript section? :) Sure you can simply remove it, but... well, you the BUT. :D