Seeing that the President just celebrated his 50th birthday this past week, this is a timely question. Certainly, I think that one can see much of his early childhood as not necessarily "good" or "bad" but as having cast a major impression on him and how he was to formulate his understanding of the world, a view that he carries with him into the political realm.
The book spends a great deal of time assessing the condition of one's heritage in the formulation of the paradigm with which they interact with the world. The condition of not knowing his father as a consistent force in his life, the reality of a biracial experience in a nation that literally saw reality in only "Black" and "White," and how living a life of "the other" are all significant events in Obama's life that ends up helping to construct how reality is both seen and understood. Another significant event that is brought out in the book is his introduction to spirituality at Trinity United Church. From a background that did not really embrace religion as part of its cosmology, Obama was immersed in the teachings of Trinity United, a church were religious zeal and intensity was evident. This helped to construct or develop a world view where religion played a vital role in one's spiritual dimension. It also helped Obama to find a bridge between his own background that the world of "the other," in terms of White America. Finally, I think that the death of his own father, the event that helped to spawn the book, is of vital importance. On a positive level, it helps to allow Obama to understand the importance of being a father to his girls. When the President makes a PSA talking about the importance of fatherhood, one understands that he speaks from a personal example of not having one. This is an example of how an effect of this event is felt. On a much more cynical level, the ghost of his father's reality is something that has to haunt Obama, something from which there is no escape. I think that this is an example of how one life event is felt in different ways.