With regards to the overall article the idea of the visual system being able to tell the difference between edges that are from the light source (shadows) and the reflectivity of objects (shapes) and then enhancing them differently in the print is a good idea. He covers this in his book as well which is a good read. I never gathered how the PercepTool did any such thing, it can't in fact. That said, some find it gives them a good starting point. It just doesn't do anything at all like what he writes is the important difference in "presence" as it has no way to distinguish lighting and reflection edges. I think this may be why a lot of people thought the tool was BS - it doesn't do what George goes on and on about. That doesn't necessarily make it useless though!
I've never understood what he's on about with the history brush. His contrived and inept demonstration of the difference between it and layers/masks here just demonstrates such a stunning lack of understanding at the basics of layers and masks in Photoshop that I have to think something got lost in the writing and the example. It doesn't seem possible George could be as clueless about layer editing as the article make him out to be, must just be poor writing or something.
The history brush is destructive editing, and that's fine if you like to edit that way. But you can trivially use masks and layers (and adjustment layers) to do exactly the same things he is doing just as easily with a non-destructive work flow that allows for later fine tuning and iteration. His comments about the History brush vs. layer editing make no sense. That said, it is a nice tutorial on the history brush - though I've always thought it to be a defunct tool compared to the non-destructive tools that are more functional and easier to use these days. What matters really is what the artist is comfortable with and there is nothing wrong with choices, so it is nice to see a history brush tutorial.
EDIT: I should also add, with regards to the History Brush section it certainly could be ineptitude on the part of the reader as well, maybe I'm just missing something