Yesterday, Microsoft released the December Community Technology Preview (CTP) of Windows Server Longhorn to a restricted group of beta testers. They are also encouraging pre-registration for Beta 3 which is scheduled for the first half of 2007. Beta 3 is planned to be feature complete and the first public beta. Final release is presumably still planned for 2H2007.
Update: It turns out that it was The Special Holiday Edition of Windows Server Longhorn. More seriously, the CTP will also be released to MSDN and Technet subscribers, but that has been delayed by the inclement weather last week in Redmond.
Update: Microsoft also rolled out a private beta of Windows Server virtualization, codenamed Viridian. A public beta is planned for the first half of 2007.