Essentially this book contains a brief description of the functions comprising an API, followed by some explanation and examples. While it is not nearly as comprehensive (or amusing) as my resident expert, it is occasionally clearer.
The book has a reasonably comprehensive scope, ranging from file APIs via processes, sockets, interprocess communications and RPC to multithreading. Obviously it can't cover these topics in depth, but each chapter serves as a useful introduction and reference point to the subject.
The examples are not too big, but sufficiently interesting to show up real issues. In addition, although no disc is included, the example programs can be downloaded via ftp.
I don't understand quite why there is a 'language overview' of C++ in the book. It covers too much in too little space to be useful. The summary of C standard functions, on the other hand, could be handy. There are a few small stylistic and coupling issues in the C++ code. For example, I/O operators are unnecessarily declared as friends - though this is such common practice that it is hard to blame the author too much.
In summary, if you are new to UNIX systems programming and are looking for a general, readable introduction, this book is probably worth looking at. Because of its comprehensive index it should also serve as a useful reference book after the initial read.