More about SQL Server Yukon
ITWriting.com has an interview with Euan Garden about what's new in SQL Server Yukon. This article has more details than many others I have seen.
Like I had suspected earlier, the XML capabilities in Yukon are really going to put the pure XML databases out-of-commission, with a native XML data type, full support for XQuery and various other XML standards, and field indexing that is "magnitudes faster" than the current performance of XML-based operations.
Microsoft also plans to ship Objectspaces with Yukon. Objectspaces is an object-relational persistence framework. You set up the mapping of objects to tables, and from then on you just call the Objectspaces API. This will likely put many object-oriented databases out-of-commission as well. There never really was a need for OO databases, it was just some vendors cashing in on the OO trend. The relational model is based on proven scientific theory, whereas OO databases were based on buzzword compliance.