Google Office: The Missing Manual has the goal of documenting every feature available in the Google apps suite. It achieves that goal, as far as I can tell, and does so in a readable way. If clarity and completeness were the only criteria I would give this book 5 stars.
But I question the usefulness of a full-blown, menu-by-menu, option-by-option reference manual for Google apps. Most features in the Google apps suites are easy to use and easy to find. Most, but not all. I would have much preferred to see a book that was task-oriented - maybe a recipe / cookbook format. And above all, a book that is much smaller. This book is too large to lay flat, so it can’t really be used as a reference manual - a failing of most computer-related books in this age of 1000 page monstrosities vying for space on the shelves at B&N.
I also read Google Apps for Dummies, a much smaller book with less comprehensive coverage, and found it to be more useful. It gives greater emphasis to some of the more difficult tasks and completely skips over obvious menu-driven tasks that you would easily figure out on your own. The very comprehensivenes of The Missing Manual prevents it from glossing over anything, so the most trivial operations are given nearly equal space with the most complex.