No immediate need right now, but thanks for the tip.
But wouldn't creating it as a subsite mean that the permissions would be at the granularity of the whole subsite - a particular set of pages and/or url heirarchy, rather than particular components or actions? The particular use case I was envisioning was setting up particular people to be administrators for different parts of the site (not site-wide admins) - e.g., one person is the calendar admin, someone else is the boards admin - but all part of one site. Maybe I need to read through the subsite docs a little more.
