I leave the main body text at the user's default...and menus, small print and headers with %...I have used px now and again to set text precisely to images, though not IIRC in the current incarnation of any site
I use em to set the various design elements to respond flexibly to the text size, so that menu blocks and so on alter to fit
I haven't so far done a print stylesheet since the site prints off perfectly in most circumstances as it is...so I don't use pt at all
For my part, I use ems for most everything, and make body text 1em - the browser default. The only exception is that when I do a print style sheet, I us inches for spacing and pt for font sizes, like I would in a word processor.
(I don't worry so much about accomodating different printers as I do about different screens. The print style sheets are usually for documents with a very narrow pre-determined audience, where I can safely assume US letter size paper.)