I dislike few buzzwords more than mockumentary, which even academics now use casually and uncritically. People often assume it's a neutral descriptive term, but unlike pseudodocumentary -- an honest and serviceable label -- mockumentary leads many to conclude that the documentary form that's being imitated is also being made fun of. Most of the works that get labeled mockumentaries are actually honoring the form, by using its techniques to make them seem more real.Rosenbaum's a tad dismissive ("buzzword"?), but having recently finished my paper on the 1960s pseudodocumentary, I more or les agree with his reading of mockumentary. As I argue in my essay, the mockumentary is less sending up documentary conventions (though it may do that secondarily) than using documentary style to play the joke straight. The humor in Spinal Tap, et. al. comes from the absurd behavior of the "social actors" against the decorum that documentary convention usually brings to social actor behavior and presentation.
I'll stick with the mockumentary label for certain comic features, as a matter of convention. Just as we can usefully employ the term "homophobia" for attitudes that strictly speaking aren't fear of gay people, so too can we call "mockumentary" films that do not mock documentary. But I'll agree with Rosenbaum on the utility of pseudodocumentary, a term I've been using, partly because of its use in the scholarship on the 1940s "semi-documentary" features of 20th-Century Fox. Not enough academics have thought through the distinction between hybrid documentary fictions that are reflexive dramas and those that function as comic features.