Define a "Doable" Pilot Project
A small deployment pilot for an audience predisposed to adopting new technologies is a good way to create a successful outcome for the SharePoint community features. Your goal is to find a community that will create an initial critical mass of information with a well-connected and vocal leader. As you deploy more broadly, users will see and benefit from this initial content and hopefully will be inspired to contribute themselves, especially if your vocal leader uses every opportunity possible to talk about the benefits.
Building support from the ground up allows you to attract rather than mandate participation. Look for a community that may already be using social technologies as a good candidate for your pilot.
An important characteristic of your pilot project is that you have a plan for demonstrating and measuring results. Don't plan for 100% participation in any social computing initiativethat's just setting yourself up for disappointment. If you select a good pilot, you're more likely to get the kind of momentum needed to be successful with a broader deployment.