I found that out the hard way with CDs too. One office had the bright idea of putting their end-of-month backups on individual CDs (good), placing each CD in a protective sleeve (good), labelled the sleeve with the month and year (good), and made absolutely sure that everyone knew what and where they were (good). The problem was they used transparent sleeves and pinned them to a notice board instead of putting them in a cupboard or safe. The sunlight panned across the board every morning and the CD coating slowly but surely deteriorated...
