Starting today when Google Calendar invitations are sent to members of a Google Group, the attendee list will automatically update as people join or leave the group. When you join a Google Group, you will be added to all of its meetings. And if you leave a group, those meetings will be removed from your calendar. Note that groups stop dynamically changing when the total number of guests in the event crosses 200.
Google Apps for Business, Education, and Government
Reference by : http://www.google.com/