Definitely recommended for more experienced users.
Users who are still "learning the basics" might feel a little lost while trying to ascertain where and why some of the tools would be used.
Beyond the Sysinternals tools there is a lot of very useful information, and examples of how these tools can be used. Even if you think you have a pretty decent grasp on what these tools do - I recommend take half an hour to check what else is available. Every time I visit this site I always end up learning something new.
Site Blog
Sysinternals Information
Sysinternals Training
Mark's Webcasts
Go on... give your brain a beating !