Having recently picked up CS5, I have used this book quite a lot. It's well indexed (a real bug-bear of mine with software textbooks) and has a lot of handy tips and tricks that you can flick through without having to start at the beginning and work your way through.
There is a lot here, from basic tasks and tools to relatively complex procedures, all easily explained and well documented. The authors have obviously thought about what the average photoshop 'dipper' needs to know and has catered for that group of people (who I suspect may be in the majority) very well. The section on using photoshop for creating web-based graphics and design is very useful and simple to understand.
The only problem I have with this book, which does show short-sightedness by the authors, is that a lot of the photos used to illustrate each tip are terrible! Surely, in a book detailing how to improve your photographs, putting in good quality pics would have been a priority, but this doesn't appear to be the case here, where grainy and boring photos are prevalent. That alone made it a 3 star review for me, otherwise it would definitely have been a high 4.