Just saw an email from Microsoft Download which I got as a participant in the Microsoft Exchange Server 2010 Beta experience. Microsoft Exchange 2010 Release Candidate is available for download now. You can download from Here.
P.S.: The download seems to unavailable currently however you can expect it available in some time. Download link page will land you to Microsoft’s Download page at this moment where you cant find the downloadable file. Wait for a while more and you should be able to download the latest version of Exchange 2010. Keep rocking and enjoy testing.