The only issue that I have with using an Exacto knife for making score lines is that not everyone has the ability to apply a LITTLE pressure to the paper with the knife. How many times have you either not gotten the score good enough or almost cut through the cardstock by putting a bit TOO much pressure? That's the benefit of using the seam ripper that I had suggested. Every pass with it results in the same exact result. Same result as with a pen, except you don't have the colored line on your paper.