It’s now available to all MSDN and Technet subscribers. Some of the great enhancements are;
– Standby Continuous Replication (SCR)
– Exchange Managment Console GUI configuration for POP/IMAP, Public Folders, Send As/Receive As, Delegation
– Move mailbox Wizard
If you would like to know more information about what is included in SP1, check the MSExchange Team’s blog post.