[@Muttonhawk] I find that any attempt at explaining 'personality' in these things tends to be inaccurate. That has more to do with ones upbringing and environment methinks, with minimal intervention from any inherent personality type (perhaps other than the generic introver/extrovert distinction, and even that can change apparantly). 
What is really interesting is their analysis of how the 'brain' of each type ticks and how it interacts wih and percieves the world around it, as well as its primary concerns etc. I'm not approaching it from a 'managment/careers' perspective, but rather, from an 'understanding oneself/self-improvement' perspective. How to avoid the alleged 'pitfalls' of those who function in such and such a way, and how to take advantage of any inherent strengths and whatnot.