I was an early adopter of Subversion after having used CVS for a little while. I've come rather late to the Git party and I wanted a book that would give me a quick, yet solid, introduction. Pragmatic Version Control using Git is just such a book. I really like the Pragmatic Programmer books as they tend to be short and easy to read. They allow me to absorb a lot of information in a very short period of time.
The first thing that struck me was the brilliant simplicity of the example code. Many books on version control use Java as a language that is easily understood by most people. Even with Java you need a fair bit of code before you've got a program that does anything, even Hello, World! Swicegood uses HTML as his example code. This is perfect because everyone can understand it easily and you only need a little to do some interesting things. The HTML example is used throughout the book, in my opinion, very successfully.
Git itself took me a little by surprise. Having a local copy of the whole repository felt a little extravagant at first and it took me a while to get my head around the idea of having to add a file every time I want to commit it, even if I've committed a previous revision. However, Swicegood explains how and why you do both of these very well and now I see the benefit of local copies of a repository and having a staging area.
Branching is key to Git and Swicegood explains it in a lot of detail. The book closes with a chapter on Subversion and CVS integration and migration with Git and a chapter on setting up a Git server. The only disappointment for me was the sparse descriptions of GUI clients. I am totally addicted to TortoiseSVN and would have liked to have seen a Git equivalent explained in some detail.
Available on the Kindle here.