Searching for God Knows What rose to the top of my reading list after I finished reading Donald Miller's popular book Blue Like Jazz. Searching is not as catchy or entertaining as Blue, but the book is a continuation of Miller's ability to think outside the box and make excellent points about Christianity in terms that stretch many in the mainstream of evangelical Christianity. To some extent, I would call Searching a book-length presentation of the message of salvation in Christ that challenges a believer in Christ to think about things they may have taken for granted or taken to be normal (or even biblical.) However, the book is not limited to a Christian audience. In the same vein as I would recommend Mere Christianity to a person who was not a believer, I would also think that a non-Christian could read and identify with much of Searching for God Knows What.
One of the more interesting themes that Miller develops throughout the book is his "lifeboat theory" concerning how we all live our lives as if we are in a lifeboat and fighting to keep other people out of it - people we deem as inferior to ourselves. We judge ourselves superior based on a number of things. For a Christian, such a view of themselves is utlimately one of pride that is contradictory to the grace of God.