This isn't just a slimming down guide. It's taking a chain saw to it and paring Windows XP down to the bare minimum! It'll give the dev's in the Windows group nightmares.
There is a valid point here in that there is a big demand out there for greater transparency of how Windows works and what's in it. For example, when software installs, I should be able to inspect everything that has happened (i.e. registry changes, files added). It should be easy to manage what runs at startup and inspect the device drivers that are running. It should be really easy to dump huge portions of Windows that are not needed. For example, just how many people really need a distributed transaction manager on their desktop?
This of course means we need a really modular Windows operating system. I know there was a project at Microsoft to do this when I left. I really hope it happens and that it's not just for ISVs. Programs should be able to easily report what services they need to run (at runtime not just install time) and let the user decide whether they really want that service installed. It requires a more sophisticated services and install manager right in the OS.
As an aside, there's also LitePC and nLite.