There are lotsa type of heatmap analyzing tools out there, most of 'em require a script that hafta be installed on yer page, in order to harvest the data, so you can see the heatmap.
But this Feng-GUI ViewFinder, is rather unique, because it have a different approach on generating the heatmap, it does not require any script at all ;)
It was based on the Salience algorithm, which i've just heard about it when i found Feng-GUI.
The ViewFinder algorithm creates a map of salience site. The charts of salience were developed during the 25 last years by the research laboratories on the numerical vision. The algorithm was developed then compared with the experimental results of research on the movements of the glance, in order to accurately represent the way in which the human ones are attracted by the visual ones.
Basically, it tried to mimic our way of looking at things around us, what is the most capturing to our eyes. It takes into account all aspect of our human eyes, contrasts, colors, textures, and they stated over their blog post that their aim of ViewFinder is to have it behave like an eye and a brain, which scans thing from top to bottom.
So, in conclusion, i think ViewFinder is a great tools to follow, since they have the beta marked on the logo ;)
And if you would want to see more, Feng-GUI lab have a video edition of how the Coca-Cola GTA video is being heated by ViewFinder attention heatmap.
Or maybe look into what they've been researchin' ;)
Oh, and incase you wanna have it, they also provide a bookmarlet too ;) Firefox-er ? No worry, they have an extension too ^^