Let me give another plug for "As They See 'Em"...very interesting and I certainly gained a new respect for the job umpires have to do....even felt bad for Jim Joyce who blew the perfect game last week.
I also had a chance to catch a Rockies game while I was in Denver last week, and actually watched the umpires, their mechanics, positioning and rotations, something I've never done before. The book gave me a new appreciation and aspect of watching the game.