I'm not quite sure why they named this one the Pocket Consultant because this book is quite a bit oversized to fit that title though still smaller than the standard sized computer book (i'm guessing the size at about 8" x 6" and about 1 1/2" thick). For those that are concerned more with the content of the book instead of actual size in relation to the title, the IIS 6.0 Administrator's Pocket Consultant should be everything you need to manage and tune IIS.
I've been in Windows server administration about 8 years, the last 3 of which for a web host. We started running Windows 2003 with IIS 6.0 since its inception early 2003. Due to the nature of what is required of me, I need as many tools as possible to help in troubleshooting and configuration of IIS from every possible aspect since I am responsible for 20,000+ web sites. IIS 6.0 is so much more different and robust than IIS 5.0 and previous versions, so there is a bit of a learning curve involved with the transition. This book will help the person that has never touched the new version of IIS as well as the veteran that has worked with it for quite some time.
It wont be the only book you need to host a single or multiple web sites, since you also need to know about .net, asp, SQL, depending on the needs of each site. This book will however provide a most if not all of what you need to take care of the actual web server portion of your duties.
For more information on Windows 2003, I also suggest Windows Server 2003 Unleased.