Exchange Server 2007 SP1

Heres the TechNet doc. About whats included in the SP1 for Exchange 2007:

What’s New in Exchange Server 2007 SP1
Microsoft Exchange Server 2007 Service Pack 1 (SP1) introduces many new features for each server role. This topic discusses the new and improved features that are added when you install Exchange 2007 SP1.

To download Exchange 2007 SP1, see Exchange Server 2007 Downloads.

New Deployment Options
Client Access Server Role Improvements
Improvements in Transport
Mailbox Server Role Improvements
High Availability
Unified Messaging Server Role Improvements
Development Improvements

Here is the full articcle: <http://technet.microsoft.com/en-us/library/bb676323.aspx>