Coincidence or not? 'Have you ever created or received XPS files' is the January poll on my site. You can vote or look at the results in the right hand column of
my page on XPS.
It isn't surprising that not a lot of people use XPS yet. The failure of Vista has been a setback for its market acceptance. The lack of a viewer and creation tools for Mac doesn't exactly help. The XPS feature set is inferior to that of PDF and it has yet to prove its reliability.
On the other hand Microsoft has proven to be both patient and able to consistently improve its products when it tries to establish a market standard. It will probably succeed in making XPS a popular solution to drive printers and share office type documents. I don't think they care about its use in the printing industry.