Nested groups?

Not sure if this is easily possible, or how widely used, but it might be good to be able to designate groups as being the parents of other groups. For example, we are planning on passing out info and recruiting members at the Erie Jazz Festival. It's an annual event, and it might be useful to set up a group Erie Jazz Festival, and the groups for succeeding years, so we could automatically know that X folks came in from the Jazz Festival (regardless of year) and X number of folks came in from the Jazz Festival for a given year.