Bumped into this very interesting guide yesterday and I believe this would be an essential guide for those who are looking into creating custom reports for SCCM. The one I like the most is there documentation of the SCCM DB Schema altogether. Well not I can't see it from SQL Server, but now we have a documented description of the Database Schema altogether.
Interested? Get it from this link
OR you can get it from my SkyDrive in case that link no longer valid.