I think it useful for helping gauge what makes people tick, remember that people lie on a spectrum. Everyone [I know] who has been through has commented that it has provided some insight into how they work. It doesn't pigeon-hole people: after all its not a psychiatric label and simply attempts to crystallize a few key traits into a manageable form. Life is spectrum and MB gets some of these key axes right.

Wasn't it Jung that defined the extrovert and the introvert?