The community itself has grown over the years. The largest segment has traditionally been comprised of the groups that have grown up around Allen, John, and myself (whereever we have been). However, a range of other groups (and individuals) have also played important roles. In the US, Ohio St. has been the most significant such group. My understanding is that they got interested because of Soar's ability to combine problem solving methods, and issue that was then critical for them in the future development of their generic-task approach to expert system construction. Other groups and individuals have become interested because of the work on cognitive modeling, expert systems and robotics. These days we generally get around 60-80 people coming to the workshops.
My understanding is that the European Soar community originated primarily out of visits by several European researchers to CMU (in particular, John Michon of the University of Groningen in the Netherlands and Richard Young at the MRC in Cambridge, England). The first European Soar workshop was held in 1988 in England. The second one was held in Groningen, and included an intensive tutorial (more recent European workshops have also tended to include tutorials, as learning to use Soar has remained an issue, particularly for those who work far from the primary sources of expertise). More recent workshops have occurred in Cambridge, Regensburg (Germany), and Nottingham. The next one is planned for Leiden (Netherlands) later this year. My understanding is that the European Soar Workshops generally attract 20-30 people. The EuroSoar community has a strong cognitive flavor, whereas the US community combines cognitive and AI flavors.
There are now over 100 sites around the world that have a copy of Soar (though we don't know how many are actually using it). The heaviest concentrations are in North America and Europe, but there is a smattering of sites in Asia and elsewhere.
Some of the major research thrusts these days within the community include autonomous agents within simulated environments, human-computer interaction, and integrated natural language abilities. Various additional aspects of learning, planning/problem-solving, production system technology, expert systems, and cognitive modeling also remain strong.
@article[CarlW91, author = "Carley, K. & Wendt, K.", title = "Electronic Mail and Scientific Communication: A study of the Soar extended research group", Journal = "Knowledge: Creation, Diffusion, Utilization", Volume = "12", year = "1991", BookPage= "One: 563", Pages = "406-440" ]