Jeff Brainard posted a the results of an IDC survey along with a Q&A with collaboration analyst Mark Levitt on the Socialtext blog.
"IDC’s 1Q07 AppStats survey, nearly a quarter of the 258 U.S. respondents reported that wikis are already in use at their organizations."
This is the only research to date we have found on the current penetration of wikis into the enterprise. Gartner predicts that 50% of companies will use wikis by 2009. Perhaps we are halfway there.