I've owned my horses for about 4 years and I've ridden for about 15 years before that, so I'm pretty well versed about horses. Of course, I'm always learning new things, too, and it's nice to have a quick reference so any ailments to make sure that I'm treating them right. It's also nice to see an expert's veiw of supplements that are available, different informative articles regarding all sorts of topics, etc.
This book would be great for a beginner. If you know pretty much nothing about horses or how to treat them, this is fairly informative and will be a little helpful at least. The authors are knowledgeable and the book is pretty well written. It's the third edition, and it's almost twice the size of the second edition (which I also have), so it has more information in it.
Unfortunately, this book isn't really that informative for me. Any time I look something up I don't really know about, it seems that there is no section on that topic or the information given is very shallow.
It may be a good quick reference if you have no mentor when you get your first horse, but you really should have some people around you that can help you out when you get your first. Also, a book is NOT a subsitute for a real veterinarian. You will need to have someone come and take a look yearly at least, and for any bad seeming ailments. I would recommend this book for the person that's THINKING about getting a horse for the first time-it may help you figure out what actions may be appropriate if your horse should run across them. It's also an ok reference for a quick fix if you need an extra check.