Mac Hacks ($19.99 e-book, $24.99 print, $27.49 combo) by Chris Seibold is packed with fun and useful OS X-themed tips for anyone looking for non-obvious ways to get more from their Mac.
Like Seibold's earlier Big Book of Apple Hacks, Mac Hacks offers ways that technically savvy readers can better take charge of their system. This volume is current, and its tips are specifically compatible with OS X Mountain Lion.
From nondestructively partitioning drives to building Mountain Lion installers on flash drives, Seibold has collected a lot of useful information into his book.
When you buy a book like this, you're essentially purchasing a condensed collection of ideas. I encourage you to stop by the O'Reilly site and look at the Table of Contents for the book, which is packed with "Oh, I didn't know you could do that!" ideas.
The book is a great gift for any Apple geek in your life. Just remember that the content tends to skew more "experienced" and less "noob."