This is a good, solid book. I don't understand some of the comments here - although not aimed at people with little programming experience, it is not impenetrable or badly written. It is not an academic textbook, but neither is it an inspirational classic. It's simply a good explanation of many of the issues involved in concurrent programming - the best I have read.
An experienced Java programmer who has already used and worried about threads could read this in a couple of days and learn a great deal - at least, I certainly did. The emphasis on patterns really helps - this is the first book I have seen that uses patterns as a tool and succeeds. They clarify the argument and let the reader decide whether they want to continue with a particular section or skip over to something more interesting.
Some of thread programming is difficult and, at least at the moment, there is no way to avoid thinking about the problem - but even in the detailed discussions of the final chapter, concentrating on particular examples, there were useful general comments.
My only criticisms are: (1) The organisation of the book wasn't as clear as it could be - it wasn't until I had read it from cover to cover that I felt I could find particular items of information. (2) There was little mention of Hoare's CSP/occam and the related Java work done at the University of Kent (I'm not an expert on this, but I found that work very useful and wished it had been discussed here). Amazon doesn't seem to like links from its pages, but I am not connected with these people and think readers here would be interested in this, so please - leave in this pointer: http://www.cs.ukc.ac.uk/projects/ofa/jcsp/ Thanks!
Incidentally, if you are hoping this is a manual for Doug Lea's respected concurrency package - it isn't. I read the book hoping it would be, but I wasn't disappointed because, once I had finished the book, I found the package (with the online docs) easy to understand. So the book complements (and funds!) the package, but isn't a manual - it's much more useful than that...