I think this is a great idea; it's what we do at Instagram and we use Huxley[0] to generate these screenshots. Keeping a set of "golden" screen shots and being able to view their history over time is awesome.
Wow, Huxley looks awesome for folks using Selenium! Looks like it can work with a list like in my article, but it can also record every click in a Selenium test. I also like the idea of including RMS distance in the diff -- makes milestone changes apparent without looking at each image. Thanks
[0] http://github.com/facebook/huxley