I have been using Photoshop on and off for many years, but I wouldn't in any way say that I was proficient on it.
So since this course/book is included on Safari, I thought I'd try it out.
It was pretty interesting. It is based on many exercises, where you start with a base file they provide, and keep doing what they you to till you get to a end result.
This is actually somewhat entertaining, and I learned quite a bit I didn't know. Exercises are easy to follow (I had a couple of instances where things just didn't work – in some cases looking online solved it).
You will not get out of this course/book being a master in Photoshop, but you will probably learn quite a bit. You would probably want to do the exercises – I doubt reading them will have anywhere near the same effect.
One thing I did not like is that mostly shortcuts were not mentioned. There is a table at the end of the book (also for the tools), but that won't get you into the habit of using them.
There is also a site you can sign on (Peachpit) which has not only the files to download, but a web version of the course, with video and quizzes. It was nice enough, but felt unnecessary for the first chapters, and was offline a couple of times I tried to use it, so I stuck to the Safari version.
Overall, I felt the book was useful and even entertaining. Most chapters are supposed to take an hour, but it usually took me around 40 minutes each, so it was around 10 hours for the whole thing.