The appendix is such a weird "organ". I remember in my anatomy and physiology class the professor stated it may have a useful purpose. He stated that the appendix may store some beneficial bacteria and may inject it into the system when needed. Kind of like the liver makes the bile and the gall bladder stores it and injects as you digest fatty foods. Not sure if there has been studies done on it.
I find Embryology to be so fascinating when look at from an evolutionary viewpoint.