I bought this book with the intention of providing some in-depth Java information for new guys starting on our project, and it looks like it will do the job. I would say it is most useful for people who know lots of C/C++ and have done a little Java, and now they want to get into networking or RMI or something like that. On the other hand, I am a pretty experienced Java programmer, and it taught me a few things.
My favourite section was the one on image producers, consumers and filters. All of the other topics are covered in quite a lot of detail. For example, there is code showing you how to access a CGI script from a Java client, and details on Java serialisation. I think no matter how experienced and hard-core you are, you won't be offended by the content of this book, and you will learn something.
I only gave it 4 stars because it takes 600+ pages to explain about twice as much as Java in a Nutshell does in 100 pages, and I spent a lot of time flicking over long listings. Despite the verbosity though, the content is all there and easy to read. I'd definitely recommend this book for the project library.