Friend and colleague Gwyn Cole has co-authored Developing WMI Solutions with Craig Tunstall, published by Addison-Wesley last week. WMI has not had much publicity but if you are administering or implementing applications it is definitely worth knowing about.
A couple of years ago I did some exploratory work into instrumenting a server application and found there was hardly any material available on how to do this, particulary regarding schema design. Gwyn's book would have been very useful with its very comprehensive coverage of schema design, implementing clients and providers, and using WMI from an administrator's point of view. The latter point is important because Microsoft have already instrumented much of their operating systems and server apps using WMI, which means you can do a lot of administration via scripting. There is even a chapter on implementing the MMC snap-ins you'll want for your management UI (please don't knock up your own management app using a tree-control, it can look so amateurish in comparison).