Peter Bond has a good article (with explanatory diagrams) that looks at communities of practice (CoP) from a biological perspective. He sees these communities as balancing between chaos and structure. The more chaotic, the more energy and innovation is evident. In chaos little gets done but as structure is added over the life of the community it loses its energy.
One inference I can make from Bond’s article is that loosely joined technologes would be more appropriate for CoP’s than single structures, like a CMS or web portal. If the nature of a CoP is temporary then it would be best to have individually-controlled pieces that can form and re-form over time. This ability is currently available from a combination of blogs, RSS, tags and feedreaders.
In my experience working with single structure CoP’s (password controlled access to a single site) I still find the much more open blogosphere is a better (more flexible) environment for community building because the tools are in the hands of the individual. This flexibility, and the absence of a controlling hand, help to maintain the balance between chaos and structure.