I agree with Gautam Ghosh here: Enterprise 2.0 will not happen without culture change.
But it's not that cultural change needs to precede Enterprise or KM 2.0. They are intertwined. As early adopters start to use social tools and adopt "2.0" thinking they will slowly influence the culture of their organizations and as they do more people will see the benefits and become involved and in turn exert a stronger influence on the culture. And through this iterative process things will change.
The pace will quicken if some proactive initiatives are undertaken - especially to create Managers 2.0 but slowly but surely I believe the culture will change hand in hand with the evolution and adoption of the tools.