Similar to what can be done with activities (http://docs.moodle.org/en/Import_course_data), i have implemented a tool to import groups from courses.
It is a patch to "course/import/groups", that extends it's functionality to allow a user to copy groups and groups members from courses he taught.
This tool copy the groups that doesn't exist on destination course based on group name, and then it copy only the members that are enrolled in the destination course.