Le Danois (thanks Thomas!) points to an extraordinary study. I'm reproducing his post here:
"A study of how Google's users look at the search result page.
A joint eye tracking study conducted by search marketing firms Enquiro and Did-it.com and eye tracking firm Eyetools has shown that the vast majority of eye tracking activity during a search happens in a triangle at the top of the search results page indicating that the areas of maximum interest create a “golden triangle.
