Even if you build it, they might not come
Simply building and deploying a social software system isn’t enough to guarentee success. Despite what Kevin Costner has been told, in reality, If you build it, they may not come. Ross Mayfield, of Social Text, and Suw Charman have proposed a reasonable strategy for software adoption over at Many-to-Many.
Both bottom-up and top-down approaches are described. My experience has been that without leadership support a system is doomed. Mainly because the leadership controls the funding and will only fund what they know to be valuable.