I'm think of buying a book on Linux to help get a grip on things like:
- Shell Scripting
- Compiling source
- Checking dependencies
- Making a secure linux box
- Working with network utilities
- Under the filesystem (eg. what files go where, what the all the files on the system in plain english)
- Troubleshooting in general
- System Maintenance
- And anything else that would concern newbie who wants to become an intermediate and then eventually a guru.
NOTE: The book must be distro neutral