I vote for printing support as well. Of course, much like opening and saving files, I would expect users to have to explicitly allow the printing to happen.
We have a product that allows clients to "print-on-demand" from an XML content repository.
We are currently limited to the layout and styling that HTML can support because our users will not accept the "heaviness" of PDFs. We are also subject to the various rendering decisions and font availability of different browsers and versions, including different headers and footers, margin sizes, and low-resolution graphics.
It would be easy to directly produce XPS on our server and send it to Silverlight. If Silverlight had the ability to print, we could produce reliable page layout, fast and high-quality output.