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Adding to what was already posted, I think that it's part of an overall Microsoft effort to migrate customers to the cloud, and Service Pack 2 has a new configuration wizard that should make it easier to configure deployments that are both at their physical location and in the cloud, as well as let the local Exchange connect to the cloud version. Remember Microsoft's Ballard said recently that MS was "all in on the Cloud".
Ars Technica had a piece about Exchange Service Pack 2 recently that explained a little about hybrid deployments: "Hybrid deployments were first introduced with the RTM release of Exchange 2010. They allow companies to migrate from on-premises Exchange installations to cloud-based ones in a piecemeal fashion. In a hybrid deployment, mailboxes, calendars, and contacts can reside locally or in the cloud; Exchange will ensure that messages are routed appropriately and shared data is available to users of both systems."