Keep in mind the following about M-B:
1) Longer questionaires are likely better than shorter for accuracy.
2) Though expressed as an either-or, it really is a continuum, ranging from a slight to extreme tendency one way or the other.
3) The results are meant to be informative, not definitive or prescriptive. They are also not meant to justify or explain specific behavior.
4) Many folks don't need to take a test to figure out their types.
The last point just illustrates that these are broad categories, and the 2nd provides for variation. I'm only slightly introverted, but I rate strongly toward intuition, thinking, and judging. That matches my behavior very well. Examples:
Two hours into a party, extroverts are ready to go find another party. Introverts want to go home and go to bed. I fall into the second category. Socializing with strangers is exhausting to me...but socializing with friends and family is not, and I have no problems with professional social interactions. That strikes me as a slight introvert tendency.
Sensers are interested in past experience, working through a problem, and looking at the facts. Intuitives are much more about inspiration, seeing the big picture, and picking out patterns. Part of my job is to pick out market trends, improve faulty processes, and generally analyze patterns, and it is the part that I enjoy. I also always see tons of options, which is a strongly intuitive behavior trait. Facts by themselves bore me.
The thinking vs. feeling aspect has to do with reason vs. emotion, and I am strongly on the reason side -- scientific method, evidence, etc. I don't vote based on who I "like," but on who I think will do the best (or least bad) job based on what I know about them. I think people should be held responsible when they break the rules. I believe in being fair, but not for cutting people slack just to be nice.
I am heavily into the judging side of things. I like schedules...I subconsciously plan what I'm going to do, and I can even get annoyed if somebody (usually a "P" type) interrupts my internal schedule with some tangent. I break down problems into organized steps and chunks to guide my work. Being a "J" is how I can be an "N" and still get things done.
The point to all this is that I believe the M-B types have utility in understanding people, even if they are not completely comprehensive. M-B doesn't touch on things like individual belief systems, nature vs. nurture arguments, or sociocultural factors, of course, but it does provide reasonably accurate guidelines for behavior in a general sense.
Even stress reactions are somewhat predictable. For example, my type (INTJ) reacts to stress by either endulging in sensory activities (watching TV, overeating) or fixating on structured tasks such as organizing shelves, etc. Without going into detail, that is pretty accurate for me -- which I would expect given that I strongly fit 3 of the 4 archtypes for INTJs.