As a member of a large organization, which encompasses dozens of individual institutions, we have many security groups which are managed by different entities. We have group administration taking place at the individual institution level, as well as organization-wide. As others in this thread have indicated, we also have external consultants, contractors, and other guests that need to be provided access as well. Nesting groups is a common practice for various products and services throughout the enterprise. Failure to support something as basic as nested groups will significantly hamper our adoption of this product. Group architectures simply lack the necessary scalability without the ability to nest them within each other.