As a Church History professor, I have found this book immensely helpful. John Allen's "Vatican 101" section explains how the Vatican is organized and how it functions, making a potentially confusing topic crystal clear. He's insightful, accurate and respectful of his subject. He makes it clear that while he himself is a practicing Catholic, he tries to maintain an objective journalistic stance toward his subject, and I think he does a really good job in this book. Allen has worked as a reporter in Rome for several years, so he really knows his subject. He's gotten a lot more attention in the last year with his coverage of the death of Pope John Paul II and the election of Benedict XV. I myself have a lot of respect for the work he does, and this book only increased my respect for him. I'd recommend this book highly.
A very good detailed account of how a Pope is elected, surpassed probably only by that of Lucien gregoire' Murder in the Vatican.