|Group calendaring means different things to different people. Possible approaches are:|
1. One shared departmental calendar to which all contribute.
2. One synched group calendar of a work-group of users.
3. Overlaid personal calendars which are merged on-the-fly.
Neither package does all of these out-of-the box. Exchange 2007 comes closer than Domino 7, but Domino 7 can be extended more readily beyond customizing "public folders" due to mail being "just another application" where all databases are applications.
In Exchange, users can create a public calendar folder and drop in calendar entries. Other users do the same thing. The result is that each accesses this shared folder that is a calendar and sees the calendar. But it's just a folder really. Alternately, Exchange lets you view individual user calendars side-by-side which can be helpful, as well. In 2007, the calendar overlay gives a view of slots used by each user which is a somewhat crude version of the Lotus Notes free-time Scheduler used when Notes users schedule meetings (or in any application where the Notes developer added a scheduler object). In addition, Exchange has a limited but cool feature of the Group Schedule which is a gathered group of users or conference room resources. What makes it cool is that you can send invitations to this whole group rather than manually build lists of meeting participants.
In Lotus Notes, the Reservations & Resource database application holds on the rooms and resources. They are added like inventory documents and then available for anyone creating new meetings. The calendar document has a nice scheduler which shows all the invited meeting participants and who has a conflict at any particular time slot. You create a group calendar by simply creating another "generic" mailbox with calendar view and give everyone in a group access to that generic account. Then people can invite that generic account to meetings or have that generic account actually "chair" the meetings and send invitations to the other users. This is also often combined with the generic account also be an "ID" (user) which receives generic / departmental mail for the work group.
Neither product syncs with a global shared calendar. On the Notes side, it is an easy process to write a custom program to crawl a list of users and add/update calendar entries to a shared calendar. A full featured 3rd party tool called OnTime Group Calendar exists which tracks Notes users and gathers up their calendars. Internally, Mindwatering uses it with their business partner Rocking Chair Software. Rocking Chair Software is a re-seller of the tool. A Google search for Exchange Group Calendars also returned 3rd party tools for Exchange.