I bought this book when I was just starting my first job in digital content and I found it really useful. It's thoughtfully written, easy to understand and provides clear advice on the basics of how to write for the web.
Whether you're writing articles, ad copy or just simple functional site instructions for the internet, there are some basic things that you need to know, or at least think about, in order to ensure you're doing the best you can for your reader / user. While some of it is instinctive, there are technical aspects that need to be taken into account when writing for the web, and this book gives a great overview of the headspace you need to be in to write online properly.
This book is just a little desktop guide - it's not a comprehensive manual - so there's a lot of ground it doesn't cover. There's not a lot in here about SEO best practice, but given the speed at which SEO trends change, and the ambiguity that surrounds what works and what doesn't when it comes to Search Engine Optimisation, it's probably a good thing that there's no serious attention given to it here.
Overall this is a great starter book, and it will make you a better internet writer, but if you've already got a couple of weeks / months commercial internet writing under your belt, you might already have learned a lot of what's contained in here on the job, hence the 4 stars rather than 5.
Personally, I'm glad I bought it anyway!