It is very important to know few very important details/truths about the CAS Array object during the planning phase of an Exchange 2010 Infrastructure.Recently Brian Day written couple of very nice blog on this, in which he has explained about it very clearly.
The articles mainly focused on the answers for below points (truth about a CAS Array),
A CAS array,
I strongly recommend you to read both his posts to understand why the above statements, explained the truths in a very simple and interesting way...
Happy Reading... :)