This is one of those books that you do not really need but some people are happier with a printed book rather than relying on the web. I am not sure that is the right way to go because Skype is still developing and so any book is out of date before it gets to the shops.
Nonetheless if you want to use Skype you might find having this book to read when you have a moment (such as when travelling to work) might open your eyes to the potential Skype has beyond being just useful for Internet telephony.
One of the things I like about Skype is its support for such things as SMS messages (text messages to mobile phones). I can quickly send a text message from my laptop when it is connected to the Internet.
If you are not already familiar with Skype, it is well worth trying it out and its basic features from computer to computer are free. Even the computer to phone connections are relatively inexpensive.
If you are a Skype user, you might browse this book in your local bookshop to see if it meets your needs, but there is nothing here that you will not be able to find for yourself by reading the information provided by its website.