Thanks to Håkon Wium Lie, we were able to convert all of the XHTML proceedings from XTech 2007 into professional quality PDFs, using only CSS for styling. The PDFs are available from the proceedings page.
Håkon used the Prince processor to do this (he's director of the company that makes it), and there's a small note on the Prince web site about how it was done. Having used XSL-FO to produce a sizeable number of large documents before, I'm very attracted by being able to use regular HTML plus CSS to format PDF versions of documents. Check out Håkon's XTech presentation, Printing the Web, for details of some of the technical issues involved.
Prince is commercial software, of course, like practically all high quality typesettings systems.
