not just feel more comfortable, need to gether data for this ...

"About halfway through the life of your shoes, you might want to buy another pair to rotate into your runs. Your shoes will last longer when you allow them to decompress and dry out between workouts. Also, having a fresh pair of shoes as a reference will help you notice when your old ones are ready to be replaced."

http://running.about.com/od/shoesapparelandgear/f/replaceshoes.htm