The interesting thing about Myers-Briggs is that while it doesn't particularly conform to current psychological theory and fails a few criteria for accuracy, it has been used well over a million times world wide and most people find it difficult to argue with the sheer range of samples gathered (and its surprising accuracy).
Another point should be noted. MBTI is a type indicator - it gives an indication of your preferred mode of operating, not a strict definition of the way you are. It readily admits that people change, people react differently based on where they are, who they are with and how they got out of bed this morning.