Found this posted on the MS Exchange team blog:

• White Paper: Continuous Replication Deep Dive: Continuous replication is a key feature of Exchange Server 2007. Read about the technical details and inner workings of continuous replication technology in this white paper.
• White Paper: Planning for Large Mailboxes with Exchange 2007: Learn how to deploy large mailboxes in your environment while also achieving high performance, high availability, and rapid recovery-all at a lower cost than with Exchange 2003.