I use Myers-Briggs in my consumer behavior class. I agree it is fairly useless as a means of predicting anyone's behavior, but to date there is no personality test that does a very good job of predicting behavior. The fact is, personality itself is such a fluid and unstable construct that attempting to categorize people based on it is ludicrous. For example, whose personality? The one you think you have? The one your best friend thinks you have? The one your mother thinks you have? People express different aspects of themselves to different people, so why wouldn't they do the same when taking a test? The idea of a fixed personality state does not jibe with the complexity of human cognition and emotion.
That said, Briggs-Myers is useful in that personality theory in psychology is based on the idea of identifying various "traits" that people have and then categorizing people based on those traits. The Briggs-Myers framework is a practical application that is easy to demonstrate and use. It is most useful in consumer behavior because brands often shape their personalities to match or be endearing to the personalities of their target markets. Examples of this abound and include everything from Ronald McDonald to the Geico Gecko.
It is true that very few practitioners use Myers-Briggs specifically, but they all use similar methodology to identify traits, and therefore Myers-Briggs has stood the test of time.