This isn't for those wanting walk-throughs of Time Machine and the more graphical side of the Mac, but it is a tamed introduction to the uglier side of Mac OS X. Tiemann cleverly garners enthusiasm for the daunting world of Terminal by immediately customising the appearance of Leopard's newly-tabbed Terminal window.
Normally fearsome Unix commands are explained in a frisky style that doesn't have you reaching for Command-Q. Plenty of reasons to use the command line are proffered, though the book also provides tips for the graphical side, highlighting integration between the two, as well as recommendations of tools for tasks such as scheduling cron jobs.
The focus upon the command line makes this a dryer offering, though there's also coverage of Disk Utility and network configuration. Thankfully it's well enough written to prevent you coming to a grinding halt, and it is a good route into the underbelly of OS X.