I purchased this book because I needed to write a debugger for Win32. While it does give hints about the necessary API calls and processes, it does not provide any source code and avoided many advanced topics. I was highly disappointed.
The book doesn't contain much detail. It covers all most important aspects of the problem and treat all architectures, processors and operating systems equally, however wery rarely spends more than one page on each of them. For example MacOS debug API is described on less than one page. The information is also quite old. There are no information on MacOS X, but plenty of information on Windows 3.1 and Windows 95. It may be a good start point if you need to know something but definitelly not a book which you would like to use all the time. Especially that there are no code sources and no examples.