As you've probably heard already, Microsoft has announced that two of the so-called "Pillars of Longhorn" are going to be supported on Windows XP and 2003 Server: Avalon and Indigo. We knew this already for Indigo but its a volte-face for Avalon because Microsoft had previously being saying that Avalon was so deeply embedded in Longhorn that it was not possible to support it on the earlier operating systems. This is good news for those of us who were looking forward to doing serious development with the WinFX and Avalon technologies but realized it might be at least 2009 or 2010 before Longhorn-only projects were started by more than a small minority of software vendors and IT departments.
WinFS will only be supported on the client and server versions of Longhorn from 2007 and I wonder whether it will be delayed even further because of performance problems. After all, Microsoft have been working on this technology since the Cairo concept of 1992 or earlier and you would have thought by now they would have sorted out the basic architecture and design. Unfortunately disk drive performance has not been improving at the same rate as CPU performance and even if it improves enough by 2007 or 2008. other applications will also take the advantage of this and may appear lightning fast in comparison to WinFS. I hope I'm wrong about this because WinFS does sound very interesting.
According to this report by Paul Thurrott its unlikely there will be another alpha release of Longhorn and the first beta will be early to mid 2005 (to coincide with the PDC slated for next year?).