Besides, it's fun to scribble notes all over printouts and Xeroxes :^)
I mark up a printout with scribbles ("hourglasses and arrows and a documentation resource for each one, sayin' what they was about, to be used in evidence against us"[*]) and then re-transcribe them into the original electronic doc. I wish I had a better approach that wasn't so environmentally destructive, but I just don't notice errors as easily when they're just on the screen.