While Chris covers a lot of important ground in the generic area of establishing and promoting group dynamics, he's clearly not specifically focused on communal software products.  That's OK, that's my part.  For open-source and inner-source communities, there also needs to be some attention to the communal dynamics of the actual product, the code.  Over at java.net (like  OpenOffice.org, another excellent Sun-sponsored, CollabNet-hosted community), they distinguish between "Community Manager" (pretty much what Chris covers) and "Community Leader."

The Community Leader is a technical contributor, who guides the technical aspects of the community. Someone has to keep discussions on-topic, to propose and manage communal conventions like coding standards, to mediate the release process, and to ensure that all these community members "scratching their own itches" still cover all the necessary bases for a complete product. The Community Leader is often the original author of the code (think Linus Torvalds and Linux, or Marc Fleury and JBoss, or Karl Fogel, Ben Collins-Sussman, and Jim Blandy of Subversion).  Sometimes, the Community Leader is a primary committer who has taken over the reins from the original author.

The most important thing about the Community Leader is that s/he must be technically involved in the project, and a credible, respected contributer. The Community Leader is an opinion leader and cultural model for the community at large. Just spend some time in the email archives of the three communities mentioned above, and you'll be amazed at how closely the community personality matches that of the founder. If you're establishing a community, you'd do well to consider the personality of anyone you consider for the Community Leader: would this personality, writ large, foster contribution, or only dissent?  This could make or break your community.