I just wanted to remind everyone about the fantastic reference that the ProjectServer 2007 SDK is. It's available for download off MSDN. Go to the Office Developer Center for Project. The content in the SDK is wide and variety and deep in context. It should be your first stop for finding information on the PSI.
Believe it or not one person is responsible for creating it. He is feverishly working on the next revison of the SDK which should be out around the end of September. It will have more descriptions, more samples, and more aritcles. The task of dcoumenting a new API is massive, so thanks for all the hard work of our tech writer Jim.