While reading the Personality Plus article, I found it very unnecessary that the faculty of the McKinsey consulting firm knew their coworkers' M.B.T.I. types by heart.  In the workplace I wouldn't focus so much on someone's personality type based off of a test.  Instead, I'd focus on how that person reacts in certain situations.  I mean, it isn't hard to gauge how someone will react after you've interacted with them enough. We do it in college with our social groups all the time.