Channel 9 has posted a great video interview and demo of how OpenXML easily allows interoperability with back-end systems on the LAMP stack. This demo was created by developers at Sonata Software who specialize in IT development and global off-shoring. The company is based in Bangalore but has clients throughout the world.
To be completely fair, this demo could probably be implemented using ODF as well but the main reason no one in there right minds would want to use ODF is that it doesn't support all the advanced functionality of the Office 2007 system. With OpenXML, developers can implement the entire specification if they wanted to and be compatible, which is not the same with ODF.