A lot of documents I create, are for both printing and onscreen publishing (.pdf). In the .pdf's, I like to add a divider to spreads, to make clear that two pages are show. When setting the 'Non Printing' Attribute for this divider, it dissappears on screen. Maybe ther should be an 'Invisible' check box for that, and a 'Non Printing' option for objects that are visible, but do not print.