I'm not into labelling, but I do think the whole introvert/extrovert continuum can be helpful for understanding how to deal with people closer to the extremes of the continuum. . .not as much for the people near the middle. I think it's also helpful for understanding organizational dynamics, if the majority of the folks lean heavily in one direction or the other. I'm shy, sometimes painfully so, but I can "flip a switch/adopt a different personna" and appear to be considerably less shy. Sometimes, it's almost like I'm having an out-of-body experience.