Performance tips of using XML data in SQL Server
Kun Cheng from SQL Server Customer Advisory Team has come up with an interesting article that points out three tips that helps you to optimize XML operations. The first tip is to use property promotion, the next is using TYPED XML and the third is using XML indexes.
http://blogs.msdn.com/sqlcat/archive/2010/03/01/performance-tips-of-using-xml-data-in-sql-server.aspx