When you look at an ant colony, it seems like there is a big brain somewhere... Lots of people don't like having structure imposed on them.
The "ants" surely do the lion's share of work to build wikipedia. But we should remember that the best practice demonstrated by Wikipedia is not the opposite of imposed structure. Far from it, the simple fact is that there is a big brain behind Wikipedia which very discretely organizes the actions of the ants:
Collectively, there are a set of rules that govern what can be done in this wiki and people who manage the structure through the list of possible categories and who enforce the rules, though sometimes with differing philosophy, but all with common governance.
As many companies are fretting with developing blogging policies (see Blogging Policy = Blabbing Policy), Wikipedia provides a good case study which includes top-down policy and structure, wherein the ants may freely work bottom-up towards the group goals. The fact is, ant colonies work effectively because there is a set of explicit or implied marching orders and a discreet division of labor between management (the Queen or Queens), workers, and other roles such as alates.
Best practice recommendations (see KM Forum and case studies from Ipsen, a global pharmaceutical company and SITA, a network provider to the airline industry) show that similar top down support and a set of structure and rules for a workspace provide a necessary framework for knowledge workers to adopt technology with willingness and efficiency.
