Rick Prelinger's Blog
Rick Prelinger is the man - the moving image archivist's archivist. Once again Scott Huffines has turned me onto an outstanding blog, Prelinger's Blackoystercatcher. Prelinger is also on Twitter (http://twitter.com/footage).
Here's Prelinger's great post about the predominance of the "narrative arc" in contemporary documentary filmmaking: Taking history back from the "storytellers"