One of the key factors in choosing CCR as your method for deploying Exchange 2007 is that people want to maintain a level of high availability and protect your data. Now CCR offers this in many ways – but depending on your deployment and indeed options within your data centre there are a number of external factors which will dictate the uptime and availability that you can get. Some interesting reading:

-Installation check list for Windows 2008 CCR Clustering
-Introduction to CCR deployment and an overview of the technology
-Introduction to CCR deployment on Windows 2008 this topic contains the meat and potatoes of CCR deployment on Windows 2008

More info: Exchange 2007 CCR