Thanks to Dominic for this detailed post on Exchange 2007 Compatibility with CRM 3.0.

It has been a definite pain for partners selling Exchange 2007 along with CRM 3.0.  But here is the reason why it is tough to make them work together without Exchange 2003:

CRM 3.0 and Exchange 2007 Compatibility by Dominic Pouzin

Best,

pk