If properly stored the media life should be far greater than 3-7 years.
Kodak have done some pretty rigourous accelerated-aging studies on their own CDRs and came up with an estimate of 217 years average lifetime. A copy of the report is online at http://www.cd-info.com/CDIC/Technology/CD-R/Media/Kodak.html if anyone's interested. Kodak's (more conservative) official position is that "under normal storage conditions", Photo CDs should last for "100 years or more."
Obviously the manufacturers of cheaper media won't have data lifetime quite as high on their list of priorities - the lifetime of unbranded budget CDRs is probably nothing like that...
S
