Microsoft has started to deliver the Release Candidate of Internet Explorer 9 via the Automatic Updates feature in Windows 7 and Windows Vista in order to update the Beta.
As reported, Microsoft wants to make it easier for the testers to switch from Beta to RC. If Windows Update is configured accordingly, the update is installed automatically. This avoids that many users continue to work with the beta version.
After the final version of Internet Explorer 9 is done, it will be sent to users of the test version as well via Windows Update. Internet Explorer 9 Final is scheduled for Q1/2011, so we can expect it before the end of March.