Eyetools Research is running an eyetracking analysis on CSS Zen Garden. Their eyetracking analysis shows where users actually look on a web page. CSS Zen Garden shows the same content (indeed, the same HTML) with multiple designs.
The nice thing about an eyetrack study of CSS Zen Garden is that it is possible to see how people react to the same exact content in different designs. So far, they have tested the original design and one other. They are taking votes for what designs to test next.
If you haven't done so yet, you might want to check out the Eyetools blog. If you are interested in CSS Zen Garden, you might want to look at the CSS Zen Garden book.