Arpan has posted good news yesterday:
One of the most frequently asked questions... where is the SPS Extranet Whitepaper? It's on its way. We expect to have it published early next calendar year on TechNet. Another topic, that is very relevant to SharePoint Extranet solutions is Best Practices for Multi-Tier SharePoint Development - specifically, how to develop Web Parts and Custom Site Definitions and move them between dev, test and production environments. That whitepaper will also be available by early next calendar year on MSDN.