Believe it or not, the respectable districts of the MBTI are backed by decades of psychometric support, as the leading Big Five psychologists (among others) have acknowledged. In fact, contrary to some of the poorly-informed MBTI "debunkings" you may have encountered in your internet wanderings, the MBTI has been found to be psychometrically "on a par" with the leading Big Five tests in the reliability and validity departments.
For more on the scientific status of the MBTI, see
this TC Wiki article.
Among the sources cited in that article is
a 2003 meta-review and large-sample study that summed up the MBTI's relative standing in the personality type field this way:
In addition to research focused on the application of the MBTI to solve applied assessment problems, a number of studies of its psychometric properties have also been performed (e.g., Harvey & Murry, 1994; Harvey, Murry, & Markham, 1994; Harvey, Murry, & Stamoulis, 1995; Johnson & Saunders, 1990; Sipps, Alexander, & Freidt, 1985; Thompson & Borrello, 1986, 1989; Tischler, 1994; Tzeng, Outcalt, Boyer, Ware, & Landis, 1984). Somewhat surprisingly, given the intensity of criticisms offered by its detractors (e.g., Pittenger, 1993), a review and meta-analysis of a large number of reliability and validity studies (Harvey, 1996) concluded that in terms of these traditional psychometric criteria, the MBTI performed quite well, being clearly on a par with results obtained using more well-accepted personality tests.
...and the authors went on to describe the results of their own 11,000-subject study, which they specifically noted were inconsistent with the notion that the MBTI was somehow of "lower psychometric quality" than Big Five (*aka* FFM) tests. They said:
In sum, although the MBTI is very widely used in organizations, with literally millions of administrations being given annually (e.g., Moore, 1987; Suplee, 1991), the criticisms of it that have been offered by its vocal detractors (e.g., Pittenger, 1993) have led some psychologists to view it as being of lower psychometric quality in comparison to more recent tests based on the FFM (e.g., McCrae & Costa, 1987). In contrast, we find the findings reported above — especially when viewed in the context of previous confirmatory factor analytic research on the MBTI, and meta-analytic reviews of MBTI reliability and validity studies (Harvey, 1996) — to provide a very firm empirical foundation that can be used to justify the use of the MBTI as a personality assessment device in applied organizational settings.
McCrae and Costa are the leading Big Five psychologists, and authors of the NEO-PI-R, and after reviewing the MBTI's history and status (including performing their own psychometric analysis) back in 1990 — using an earlier version of the MBTI (Form G) than the one being used today —
they concluded that the MBTI and the Big Five might each have things to teach the other, approvingly pointed to the MBTI's "extensive empirical literature," and suggested that their fellow Big Five typologists could benefit by reviewing MBTI studies for additional insights into the four dimensions of personality that the two typologies essentially share, as well as "valuable replications" of Big Five studies.