Mixed Reality Architecture (MRA) supports distributed teams in their everyday work activities by linking multiple physical spaces across a shared three-dimensional virtual world. User configurable audio-visual connections give the inhabitants of MRA full control over whom they want to be in contact with and when they make themselves available, as well as over the overall configuration. We report on the design of MRA, its deployment in an office environment and results from a long-term observational study. The study shows that MRA supports the management of awareness, social interaction and privacy well, that the architectural design features are crucial for this process and that the dynamic architectural topology of MRA and social interaction within it are linked in a fundamental way. Categories and Subject Descriptors H.5.3 [INFORMATION INTERFACES AND PRESENTATION (e.g., HCI)]: Group and Organization Interfaces --- Computersupported cooperative work, Synchronous interaction, Evaluati...