Rating: 

Well structured with thorough examples that you can almost cut and paste together to create complete programs.

It should be noted however that this book is about programming using system calls to the OS. It is not about GUIs or other abstracted programming environments.

Typical examples of OS programming include

Shared memory, Signal handlers, Inter Process Communication (IPC), File handling, process management, terminal management, TCP/IP client/server communication.

Oh yeah, the coding principles are well documented and pretty much portable (with minor tweaks).