The recoverability solutions in Exchange Server 2007 are the features that I am the most excited about. The original release of Exchange 2007 not only included support for the same clustering model as earlier versions of Exchange (now called single copy clustering, or SCC), but Microsoft also introduced a new replication technology. The new technology can be used in a few different configurations to replicate a copy of the Exchange databases.
The replication technology in Exchange 2007 RTM (release to manufacturing) was applied to local continuous replication (LCR), which allows you to keep a local copy of the database. The RTM replication technology was also applied to a new clustering technology called cluster continuous replication (CCR), which allows a two-node cluster to always have a replicated copy of the active cluster node's databases.
Another new feature that uses the same replication technology is called standby continuous replication (SCR), which allows you to replicate a database to another Exchange 2007 SP1 Mailbox server entirely. SCR is designed to help organizations that want to improve their service resiliency, not necessarily their availability.
At this point in the life span of Exchange Server 2007, I have implemented all of these technologies and I am impressed with the ease of enabling a complicated feature such as LCR or SCR. Even CCR, which requires some knowledge of Windows clustering, is much simpler to implement ...