So how is it going to work with Exchange 2010? DAGs still use some features of Windows clustering for the heartbeat and quorum, so the new Active Manager can manage a failover in case one of the DAG nodes crashes. There is also database level failover (and switchover). It's not just for server crashes but any failures that affect an active database can be dealt with (within 30 seconds) by Active Manager. You still need the Enterprise Edition (or Datacenter Edition) of Windows Server for some of those clustering features to work, but you don't have to stress out about setting up the cluster before you install the Mailbox role. (For those of you who have configured CCR, you know what I mean about setting up the server, getting the cluster in place, and then doing the installation of the Active Mailbox role.) Instead, when you add the first MBX server to the DAG WFC is automagically added behind the scenes.
With a DAG you can have up to 16 copies of a database (how is that for resilience?) and install other server roles on a server that is a member of a DAG. In contrast, with CCR, you had to isolate your active and passive MBX servers from other server roles. Speaking of resilience, DAG members can be located on different subnets and in different Active Directory sites, although this doesn't differentiate what could be done with CCR because you can have CCR on Windows 2008 that can be on different subnets and SCR allowed you to replicate to a separate AD site.
Let's recap: Storage groups, single-copy clusters, SCR, CCR, and LCR are all gone. What remains are databases that become the main focus beyond storage groups; continuous replication with asynchronous log shipping through DAGs to provide for disk, server, and site (or datacenter) resiliency; and cheaper storage solutions like JBOD to help you reduce cost, improve mailbox sizes, and increase performance.
Stay tuned for more!