From a ComputerWorld Article:

http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9026039&intsrc=news_ts_head

Standards body ECMA International has formed a technical committee to develop a standard built on Microsoft Corp.'s XML Paper Specification (XPS), a rival file format to Adobe Systems Inc.'s Portable Document Format (PDF).

According to ECMA's Web site, the goal of the TC46-XPS Technical Committee is to create "a formal standard for an XML-based electronic paper format and XML-based page description language which is consistent with existing implementations of the format called the XML Paper Specification."

I gotta say, a standard in this area is long overdue. Anyone who has labored to generate or parse a PDF doc, in any language or platform, would probably agree.  I've done it in PHP, in Java, and in C# / .NET, and it's never very easy.  With a standard here, any app will be able to easily generate, parse, and modify the XPS.