Kirk Evans is a Microsoft Architect for the Azure Center of Excellence.
Introduction to SharePoint and Azure IaaS
Building SharePoint Apps with Windows Azure Platform as a Service
SharePoint Solutions and Architectures on Windows Azure Infrastructure Services
Understanding Authentication and Permissions with Apps for SharePoint and Office
If you currently have code that uses XSLT and you are anticipating a move to Whidbey, be advised that the XslTransform class is obsoleted, replaced by XsltCommand. The XsltArgumentList class will continue to live for passing parameters to XSLT stylesheets.
Note also that the .NET Framework 2.0 will not ship with an XQuery implementation. There will continue to be XQuery support in SQL Server 2005, code-named "Yukon".
For more information on the changes in System.Xml, see the list of changes in Beta 2 by Dare Obasanjo, PM for System.Xml.