Yes, whether being stored in a jewel case or a sleeve, it would be best to store them upright. See the excerpt below. In 2004, scientists at the National Institute of Standards and Technology (NIST) looked at CDs and DVDs to see how long digital information recorded on to them would survive. They concluded that most CDs and DVDs will last 30 years under ideal conditions, but many things can make them unreadable. Direct exposure to sunlight can do it; so can heat. Discs last longest when stored in plastic cases in a cool, dark, dry environment. Because gravity can gradually bend the disc, storing it upright like a book is best. The study also found that fingerprints and smudges frequently do more damage than scratches, and recommends handling discs by the outer edge or the center hole. For more information: http://www.itl.nist.gov/div895/carefordisc/CDandDVDCareandHandlingGuide.pdf
