Adam Greco has always been an authority on SiteCatalyst, but what makes this book stand out is his style. Very easy to understand, very complete, very focused on accessibility (in the sense of: right, I'll try that _right now_!).
In fact its the only text. Densely packed with information from Adam's blog you will find yourself reading certain sections over and over again, keeping it as a handy reference guide. My (well worn) copy is om my desk at all times, indeed I bought 20 copies for my organisation, which quickly vanished!