Love xkcd. Spherical cows and all that. But appropriate parsimony is a desirable feature. Here's a summary of whether the equation does a good job of summarizing the science:
http://studiemetro.au.dk/fileadmin/www.studiemetro.au.dk/Procrastination_2.pdf
Also, from the book "The Procrastination Equation"
The Procrastination Equation attempts to economically describe the underlying neurobiology that creates procrastination. I will tell you right now; the biology and the math won’t match exactly. A road map of a city, for example, no matter how recent or detailed, can’t represent every corner and crevasse of reality; it skips over details like architectural styles or fire hydrant placement. Judiciously focusing on streets and highways allows the map to emphasize navigation. If this big picture doesn’t satisfy you and you want all the details, don’t fret. The next chapter will give you what you are looking for.
The next chapter discusses it from a neurobiological perspective, which ultimately provides deeper understanding. I think as along as people recognize the purpose of the equation, and that it actually is a step up in complexity from what was previously used, as well as not mistaking the map for the land, it works.
Lukeprog has written an excellent summary of The Procrastination Equation by Piers Steel. However, since everybody has a different style that they enjoy, I thought I'd post my own summary in the style that I like best: the bullet-point outline. In fact I'm hoping this post can also serve as a test of whether others find this style useful as well. So please comment on the style as well as on the content.
Disclaimers
The Procrastination Equation
Reasons for procrastination with suggestions for improvement:
Other suggestions
Some other procrastination resources: [this part's not from the book]