wlach commented on my INTJ posting to mention that this sort of thing is often just telling you what you want to hear, so of course it sounds believable. Certainly there are plenty of "personality tests" and other things out there (astrology, anyone?) that do this on purpose in order to manipulate you, but the Myers-Briggs and Keirsey personality descriptions are different. They're just too specific to be able to fall for this problem.
Especially in the case of INTJ, sure, it says a lot of nice stuff, but it says a lot of specific stuff that not only fails to apply to almost everyone, but also that most people would find violently opposed to their self-image. "This self-confidence, sometimes mistaken for arrogance by the less-decisive..." and "INTJs have also been known to take it upon themselves to implement critical decisions without consulting their supervisors or co-workers." These are simply not generic statements. They're not true of almost everybody.
Moreover, all the other personality type descriptions I read, which all try to say as many nice things as possible ("accentuate the positive," you could say), simply don't match me nearly as well. In other words, a highly accurate personality description was attached to me automatically by a 76-question multiple choice quiz. That's pretty cool.
But I already know a lot about myself. The really interesting thing is slotting other people into their own types and realizing why you've had trouble dealing with them, and then what you can do about it now that you know.