One of the difficulties of Linux is that, like most software, certain technical details change all of the time because software maintainers change, they implement new features, and they can be just plain fickle. Although this book strives to cover topics that have some degree of stability, it's impossible to tell the future. The good news is that the base system really doesn't change much. Concentrate on what the system components do , not the details of every strange little option. Remember that the online documentation is always there. In many cases, learning the correct terminology is more important than learning the actual details, because it's the terminology that helps you in your search for the documentation.
Linux (and Unix in general) doesn't exist in a vacuum . There are a lot of people out there who can help you. A few examples are IRC channels, mailing lists, user groups (check http://www.linux.org/groups/), and the USENIX/SAGE organizations (http://www.usenix.org/). USENIX has been around since the early days of Unix (incidentally, if you're interested in "the old days," you should read A Quarter Century of UNIX [Salus]).
Keeping your system simple and clean helps when tracking problems. Don't get obsessed with it, though ” zealously removing " errant " files can be harmful .
Finally, don't be afraid to try new stuff!