"The scientists working on the Digital Preservation Program at the National Institute of Standards and Technology (NIST) has released an excellent 50 page guide on care and handling of CDs and DVDs for long term storage. It talks about the effects of light, moisture, radiation, scratches, marking, adhesive labels, and even playback on the discs. For those who are not familiar with the physical make up of these optical discs, there is a very nice chapter explaining all the background. And if you only want to know how to care for your precious data, this is a one page summary:
http://www.itl.nist.gov/div895/carefordisc/onepage.pdf
http://www.itl.nist.gov/div895/carefordisc/onepage.pdf