The slides for my recent presentation (on file system abstraction) at DotNetNuke World 2011 are located here. Note that there are several changes here that are not realized in the slides available through the conference site, though these are primarily pedagogical in nature.
I will be releasing the source for the cross-portal symbolic link folder provider later this week. Note that, for URIs that are processed via the link-click handler, this provider relies upon a yet-unreleased fix in 6.1.2. For ordinary direct-access URIs the provider functions as expected.