I found this bok an extremely helpful tool in thinking through small group principles and methods. Donahue and Robinson are both Willow Creek gurus and bring years of (sometimes painful) experience to the book. Though most reading this book will have a much smaller ministry scope than WIllow Creek, the principles nevertheless apply: (1) have clear ministry objectives, (2) Pick the right point man, (3) Develop a healthy coaching structure, (4) Develop new leaders constantly, (5) Open-group (this one is debated), (6) Broaden your definition of small group to connect with the most people (again, debatable), and (7) Think hard about assimilation and retention.
I learned a great deal from this book and will look back to it often!