One of the more valuable books/whitepapers to come out of ESRI is Dave Peter’s System Design Strategies. I think it is natural for this whitepaper to evolve into wiki format and ESRI clearly agrees.

One really valuable outcome from this is that the content now has a Creative Commons license that means that you can leverage the work as long as you attribute and share alike. I know planning GIS is a tough nut to crack, but a collaborative effort to improve the design process will improve all implementations no matter if they are ESRI, PBBI or OSGeo.