Yeah anytime I've gotten frustrated with it, it has been because, first of all, I didn't understand introversion and extroversion, and well I didn't understand a lot of it at first...I was quite lost...and the whole process of learning it and the cognitive dissonance alone can probably cause some people to reject it.
Then I got mad at Keirsey because I sound like a cross between NFP and SFP, and furthermore, now by one of the Jungian systems I look like an ES(F) Cultural Realist...and in Beebe's theory I could easily be ESFP while in Lenore's I fit ENFP just fine.
If I wasn't happy thinking "oh well I can be ExFP" I might freak out. But I'm not gonna do that.
I accept that it's just a theory, and the theory isn't going to quite fit real life, even though it may be very close.
On the other hand, I think the theory is valid enough to be approximately correct in most cases, and is a valuable tool for self-understanding, as well as understanding others.