We recently posted a bunch of sample XPS documents. Download them here. These are primarily for people building XPS solutions for the purpose of testing. The docs are designed to exercise all of the different parts of XPS. Hopefully soon we will get some 'good looking' docs posted that show real-life examples of XPS docs. Also, the markup compatibility spec is now posted. It was formerly in the appendix of the OPC spec and is now seperated out into its' own spec.