Typical files are not only too coarse, they are probably not hard enough to cut good steel. It's all about consistent blade angle and grit rating. I'm old-school and have yet to examine ceramic rods and diamond sharpeners. I've heard they're great. I too would like to hear from others on this subject.

Check out this site, it's probably the best I have found on sharpening knives, complete with notations on various sharpeners and techniques. How to Sharpen Knives

After reading this I may choose to rethink the sharpeners I have in my BOBs. It seems there's no sense in carrying stones of any type anymore except maybe for sharpening an axe or hatchet.