We argue that design for sustainable digital communities must attend to the ways that the technological infrastructure is transformed by, and in turn transforms, human communicative organisation. We present evidence from a user-contributed ‘talker’ environment, TCZ, whose infrastructure and community of users have evolved over a ten-year period. TCZ is a text-based environment built on a spatial metaphor that is incorporated both into the structure of the environment and into the operation of commands. We describe a comparison of the communicative organisation of the virtual interactions in TCZ with those typical of informal face-to-face conversations. The results show that users exploit the flexibility of the online environment to overcome the constraints that spatial organisation normally place on the configuration of their communicative interactions. We highlight the limitations of the spatial metaphor as an organising architecture for online communities and identify five communication-oriented issues for design.