Past Joshua made note of some book excerpts. Can't remember why... but I'm typing them out here in case I remember, then Future Joshua can write the blog post he intended to :) 

Edit: ohhh, these are from Drive, by Daniel Pink (link below)

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A startup engineer must be all things -- he (or she) is a full time software developer and part time product manager/customer support guru/internal systems maven. As a company grows, an engineer spends less time building the things he personally wants in the product. Our hope is that 20% time gives engineers back dedicated stack time -- of their own direction -- to spend on product innovation, features, plugins, fixes or additions that they think are the most important…