Sitewide Group Calendar

I'd like to aggregate events from a selected number of Group Calendars and display the results in a widget or page. Come to think of it, automatically displaying events as posts sequentially in an 'Events' blog would also be useful.

It would be an effective way to show all events that are happening and it gives the individual group some promotional benefit from displaying their event to the entire community.

Ideally, the event settings would allow for displaying the event in only the group or sitewide as well.