The Save as PDF... feature is fantastic; really fast, simply, no printer drivers.
Just one thing, saving the original URL information would be great. Without the source URL, the PDF feels a bit detached. As a reader, I'm not sure from where the PDF came (was this a document someone wrote? was this taken from somewhere else?). As the reader wanting to learn more, I can't get back to the original source material to explore further.
Having the source URL of the PDF unobtrusively in the header or footer would provide helpful context. This is common all other PDF printers (FoxIt PDF Printer, Microsoft PDF Printer, ghostprint, etc.).
(Additionally, perhaps the datetime the PDF was printed? okay, that's two things!)