There is an old quote "If you want to Learn Ubuntu use Ubuntu, if you want to learn Linux use Slackware". That is what really pushed me into Linux, I decided while in college one day to remove all windows systems and replace them with Slackware (when I was only using windows), this forced me to learn everything from scratch in order to satisfy my daily needs. This is an extreme way to learn quickly, but it also works providing that you do not just revert.
In the world of Unix and computers in general all books are out-of-date before they are published. MY honest recommendation is to reimage your primary workstation at home with only a Linux Distro and rely on finding mailing-list and forum posts for direction as they will be the most current and relevant.
To learn the guts and administration the best way to learn is from a less "new user" oriented distribution such as Arch, Gentoo, Debian or Slackware. All of the listed distro can do everything that Ubuntu can but in these cases you must do the research and legwork to get things running, with that you also feel the satisfaction of learning about the core and how everything fits together.