Longhorn was the big story at PDC2003.  WinFS looks exciting, Avalon has potential, but I think Indigo will have the most wide spread and far reaching effect on developers.  Even open source developers who have created other CLI implementations are taking interest in Indigo.  Here is some of the latest info:

• Is Remoting Dead? – by the leading remoting author
• Indigo Overview
• Living La Vida Longhorn
• "Longhorn" SDK
• Indigo
• http://msdn.microsoft.com/longhorn/understanding/pillars/indigo/default.aspx?pull=/library/en-us/dnlong/html/indigofaq1.asp
• http://www.peterprovost.org/weblog/PermaLink.aspx?guid=be526337-085e-4935-9f25-d641c193aab3
• http://msdn.microsoft.com/Longhorn/understanding/mag/default.aspx?pull=/msdnmag/issues/04/01/Indigo/default.aspx
• http://www.longhornblogs.com/
• http://discuss.develop.com/longhorn.html
• http://msdn.microsoft.com/events/pdc/agendaandsessions/sessions/default.aspx