Look out for XPS printers, starting with consumers
It is just possible that the Adobe take on XML has something to do with Vista. I am not suggesting Microsoft is convincing entirely on support for open source, but the possibility seems to be there to work from XML to hard copy. It seems really strange that Adobe have not promoted Mars more widely or released it as part of Acrobat 8, launched not that long ago.
Google News searches show Global Graphics with a very low profile. However there is a hint on CNET that XPS printers will appear at the Consumer Electronics Show this week. In November Global Graphics "announced it has signed a contract with HP for the provision of certain printing technologies, which Global Graphics considers to be a major contract. In accordance with applicable contractual provisions, specific terms of the contract shall not be disclosed."
More will become clear at some point, presumably. As printers become available that work with XPS there will be more debate about XML and PDF. Whether someting is open source is something that can be tested.