I have successfully repaired scratches on my iPod and HTC Evo 4G screens using a buffing compound specific to touch screen panels. They have different types depending upon the material that composes the screen so newer products with gorilla glass are repairable as well. Here's what they have available...
[http://www.tdillctechnology.com/store/accessories/resurfacing-compound.html|TDI-LLC Resurfacing Compounds]
You can find many forum posts regarding different creative ways to make the scratches more noticeable, but I have found their polishing compound to work wonders for me. It ended the my guessing game by simply working.