I came across a useful free tool for creating heatmaps of your website design at Feng Gui.   The site allows you to type in your url or upload an image and it creates a heatmap based on what it thinks a real human would be most likely to look at.  The application uses a ViewFinder algorithm to create a saliency map based on objects in the field of view that stand out relative to neighboring items. 

Recently Feng GUI released the results of a study that they say proves the accuracy of the application.  According to the study, the heat maps produced capture 70% of what a traditional eye and mouse tracking application would show. 

I see this tool being useful for early and often testing of new layouts and designs.  Because it’s much quicker and cheaper than running a eye tracking test with multiple subjects, you can use this application at each iteration of a design to see if you are getting the desired results.   I don’t think it can be a true replacement for eye tracking, as the heat map only produces a static moment in time showing the highest areas of interest.   It doesn’t give you any insight whether humans will have difficulty navigating your site, understanding your product details pages or filling out the checkout form at the end of a transaction.