I may sound harsh, but I think manuals are going to disappear due to digital delivery, or at least they're going to be needed less... It's something like artisans who don't find work anymore...
...wait, I didn't think that even if the manual is digital, someone should make it.
Anyway I'd like to have different manual layout based on whether the manual is going to be read on a screen or printed. I think screen reading needs a lot of patience and in the case of long text pdf files it takes also a good sight.
I had this problem when trying to read The 2008 Career Guide
by this very site: I was on my bed (wireless mouse) and couldn't read it even if I zoomed for the width of the page.
Bottom line: manual creators should output 2 layouts: one for the printed guide, one for the screen one (horizontal layout, in this case).