I think the article by Etienne Wenger and William Snyder called Communities of Practice: the organizational frontier is still a very good basic article, talking about corporate communities of practice. Since it's a Harvard Business Review article I didn't think it would be available on the web, but it is!
It is this article which inspired me and other members of a community of practice of advisor from SNV in West Africa some 5 years ago because it explains the differences between a community of practice and a work group/ project team and informal network so clearly. And it helped us see we wanted a community of practice whereas the management had more a sort work group or task force in mind, so it supported us in clarifying our ideas and understanding the differences. It supported a shift in the membership to include more of the advisory practitioners with similar practices in different countries.
A community of practice is held together by passion, commitment and identification with the group's expertise, and hence membership should be voluntary (at least not appointed). Whereas a work group may be appointed and the task and deadline clearly identified and monitored by a management. This leads to the management paradox: management has less control over a community of practice. A community of practice has to develop measures to show the (often intangible) benefits as compared to the preconceived tangible outputs of a project team ('set up a training and prepare a module' type of instruction). And although communities of practice are informal and self-organizing, they benefit from cultivation by management which can identify them, provide the infrastructure and use nontraditional methods to measure value. This doesn't mean that management can not give any instructions, ideas, or tasks but managers have to be skilled in energizing the community rather de-energizing it.
More and more I'm seeing the parallel of this management paradox for inter-organisational communities of practice: the agency or organisation(s) funding/advising the community of practice will also have to struggle with a similar management paradox.