This is not to mention the fact that if you change the page (unless Clixpy has some provision for this), your old recordings are entirely useless.
With regards to accuracy, ignoring the aforementioned problems: a script like this can be fairly accurate, and the actual "recording technology" behind this is fairly simple (albeit still interesting). The data can be useful, provided you enjoy wading through many, many very unhelpful recordings.
The real challenge, and what I believe is more useful, is extracting and distilling the data into heatmaps, graphs, and the like. This would provide someone with more of an overview based on the recoded data (think CrazyEgg, but even more in depth). This is something which I am working to solve, as is -- as someone else mentioned -- ClickTale.
Regardless, I commend Clixpy for diving into this space.