This book skips most of the "basics" of the Mac OS and discusses, instead, issues like data security, working with a portable as your "desktop replacement" and getting acccess to data while you're on the road. There's also troubleshooting info, a guide to portable bags and accessories and more. Plus, the publisher makes it pretty easy to buy this book, thanks to a coupon good for two Audible.com eBooks that are worth the cover price.
And that doesn't even take into consideration the fact that Amazon gives you 32% off!