I've been working on some print stylesheets, and I think it would be very handy if it were possible to switch the media type in the Develop menu or something. Being able to switch between *, screen, print, handheld, projection etc will really help in supporting those platforms I think. Even if some are not that well supported in the world, at least this change might make development of such stylesheets more accessible to website developers.
*** This bug has been marked as a duplicate of bug 13530 ***