Ok, thanks for the responses.
The MBTI types are not bullshit. If you measure your personality along four axes, you can use those four attributes to describe your personality in broad strokes. Clearly this works to some extent... for instance, the description of an INTP fits me (perfectly), while the description of an ESFJ does not (to say the least). In this respect MBTI is just like the more scientifically accepted Big 5, and the four MBTI axes even correspond nicely to four of the Big 5 axes.
The part that's bullshit is the cognitive functions. This whole subtheory seems to be an ugly mix of pop psychology, some arcane numerology, and a dogmatic reading of Jung (who wrote a lot of bullshit to begin with).
Conclusion: MBTI is at least partially bullshit, but it's interesting anyway. The Big 5 seems a lot more useful to me but it's got one big disadvantage: nobody wants to talk about how neurotic they are. The MBTI is less invasive.
Edit: That said... I think I really showed my type (INtP) by starting this thread. Google "MBTI bullshit" and you get a thread from an INFP site, a thread from an INTP site, and this one.
