Fortunately, Kiersey's isn't the only book out there trying to systemitize human nature. Don Riso and Russ Hudson have spent careers working with the enneagram, and laid out nine personality types. More interestingly to me, they have laid out for each of their nine types nine layers of functionality--ranging from extremely healthy to extremely dysfunctional. They investigate the different ways that people "integrate" (become healthier) and "dis-integrate" (become less healthy) and how that looks different for different types.
These two systems, taken together with a good dose of good theology and discretion seem to me to provide a great base for self-understanding and relationship building. I have no use for Riso and Hudson's assumption that our personalities are primarily determined by how our relationships with our parents were screwed up as very young children. I think Kiersey is more right that our general bent is stamped on our DNA. I agree with Riso and Hudson, however, that while each of us have particular driving fears and weaknesses, that we do not have to accept those as inevitable. That in fact each of us can "change" and grow in such a way as to become more fully ourselves.
Of course, none of these secular psychologists have much use for Jesus, or for sin and redemption language. But I figure it like this. God made each of us to be someone very particular. We can indeed grow more and more into the people that God intended and intends us to be. The wisdom and recognition and fear-conquering that is necessary for that growth, truly comes through Christ. Additionally, each personality type will gravitate towards particular areas of sin. This is a true marker of personality, on the one hand, but it is not a true indicator of who we are supposed to be.
I highly recommend both Please Understand Me and Personality Types for . . . well, anyone really. Particularly, I've heard a from numerous people over the past year and more who have looked up after an extended amount of time in churches where there were very specific and restrictive ideas about gender roles and marriage, and have realized that those teachings had done nothing to help their own growth as a person or as a spouse. In order to love our husband or wife we must first know them . . . if we are to help each other grow into the individuals and body that Christ calls us to be, shouldn't we first understand what will be helpful for growth?
(Side Note / Addendum: Also valuable for parenting--if nothing else, starting with the assumption that my children are going to be whoever they're going to be, and that it's within my power to break and harm them--but not necessarilly change them--is very humbling, and useful for bringing any number of parenting issues into focus.)