Microsoft has announced the first public beta of the 'Vail' revision of Windows Home Server. It can be downloaded via the Microsoft Connect site.
This latest version is based on Windows Server 2008 R2 code, a major upgrade from the current version that is based on Windows Server 2003 SP2, and comes not long after Microsoft released Power Pack 3 update for WHS that added Windows 7 integration.
One major change is that it is only offered in 64-bit form - the current WHS is a 32-bit OS. I'm downloading the preview now and will be taking a look at it and reporting back here as soon as I get chance.
[UPDATE 4th May: Here's my First Take article on Vail written for ZDNet UK]