There are a number of great resources out there relating to the proper care and handling of disc-based media, as well as resources and guides regarding the various grades and sources of disc-based media. Below are few related links you may find helpful:

Care and Handling of CDs and DVDs: A Guide for Librarians and Archivists (NIST/CLIR, 2003 – HTML)

Blank DVD Media Quality Review (DigitalFAQ.com)

If you're already familiar with these and/or other similar resources, consider taking a moment to share them with your peers and colleagues. If they're already familiar with them, feel free to blame me for the redundancy. I'd much rather deal with that than having to tell a prosecutor or investigator that they destoryed their own MASTER evidence.