This talk covered what's new in System.Xml in Whidbey. There have been quite a few performance enhancements and usability improvements that will make working with XML faster and easier. Plus SqlXml has been integrated into the System.Xml stack. I'm not sure if people made the connection, but this means that SqlXml is now using fully managed code and not the COM Interop code that is provided with SqlXml 3.0.
Performance Improvements
Usability Improvements
XmlDocument is Dead!
XQuery
SqlXml
Disconnected Scenarios
Xml Editor Enhancements