After you try using Martin Yale StakCut Rotary Trimmers, you'll swear that there is no easier way to cut paper. Martin Yale StakCut Rotary Trimmers are so easy to use that pratically anyone can use them to cut some of the straightest, most accurate lines available. All you need to do is to line up your paper along the line indicated the size you want, feed the paper under the arm, and move the cutter over the paper, and your cut is made. Not only does this method guarantee that your cut is straight and of the size you want, but there are no blemished in the line on you paper either. When you're done, you just pull the paper off the base, and you're done and ready for the next one.
(I've used these things myself tons of times. They're wonderful.)