"Selenium Testing Tools Cookbook" covers a lot of ground. I've written some Selenium tests and still learned new things in chapter 1.
It's not meant to be an introduction book so you should have written a test before. I like the depth on foundations though. From browser plugins to advanced selectors, there is a lot to see. I particularly liked the CSS selector syntax summary.
It was good to see JSExecutor covered - I wasted a good amount of time with this on a problem in the past. I liked seeing the page object pattern (which looks like a DSL) and the Actions framework. I like the example of a parameterized test case in chapter 4. I would have liked to see it broken up so not a ton of code in a row though.
There are warnings as needed when showing a feature that you might not want to use. Or when showing a feature that is only available in some cases. For example, the HtmlUnitDriver doesn't support taking screenshots.
I could write a review without mentioning the JDBC example has a resource leak. It may be "just" test code, but I still remember the time (a decade ago) that I locked out the test database server because my integration test had a resource leak in it.
I was skeptical when the book said it covered Java, C#, Python and Ruby. But it really does. This book is going to be a helpful reference to have around when I'm writing future tests.