We’ve just updated the Beta version of the cross-forest certificate enrollment white paper. In addition to fixing some of the bugs we had in the previous version, we’ve added sections around supporting selective authentication, enrollment web pages, and provided a script to delete PKI objects from AD. This is pretty much the final version. It may get edited and formatted based on the latest doc template before it gets onto the TechNet site, but the technical content is complete. The paper can be found in the same location: http://go.microsoft.com/fwlink/?LinkId=139681 . Enjoy!