I hope you guys don't mind if I add my 5 cents worth.
I think what your looking at is heatmapping, its a little server side code/program that works with a clients web browser to monitor where clicks are made on your page.
The above is the Predator type image the program generates, which clearly shows the hot spots on the page.
Keep in mind this is a heat map of probably hundreds or even thousands of clicks, and no its not mine (I wish!).
Seriously though this kind of monitoring is only really worth while when you have some serious traffic, if your just developing an understanding in optimizing adsense ads ie color and placement, in my opinion nothing beats manual experimentation followed by monitoring your analytics data (CTR).
Also I seriously suggest you mix things up a bit when monetizing your blogs.
Don't write off affiliate products!
Especially new products that just have become available, or if you think a 'trend'
Google Trends might give your niche a possible windfall of targeted traffic.
Generally speaking the hot spots are just below the header and down the right side of the page.
Anyway here's the link for the program,
Click Heat
Inside Adsense
Blue Fox