Not much after the technical previews and beta versions Microsoft released Exchange Server 2010 RC. Here is info from Technet.
Exchange Server 2010 Release Candidate is now feature complete and available for download here. New in the RC release is support for Windows Server 2008 and Windows Server 2008 R2, co-existence with Exchange Server 2007 and Exchange Server 2003, and an· in-place upgrade from Exchange Server 2010 Release Candidate to Exchange Server 2010 RTM so you won’t need to reinstall your servers or reconfigure your Exchange settings once you have deployed the Release Candidate.
Visit "What’s new in Exchange 2010" on TechNet for additional technical details.