Good shelf life, sorta low density, though.
I just encrypt my data, upload it to P2P networks as "Jessica Simpson Home Porn Video", and let horny geeks mirror my backups for eternity.
Hard disk drives keep growing fast enough, and their per-bit cost coming down fast enough, that one should instead keep all data, all versions of all files that anyone might ever care about, on ones disk drive, forever.
Offline storage still has its uses, for disaster recover and for data transportation. But don't use it instead of online storage (don't put your only copy of some useful data on a CD), and don't use it for versioning (keeping track of old versions of stuff.)
I've got stuff dating back 12 years right on my disk in front of me, including from the times I ran DOS, 4DOS, Windows 3.1, OS/2 Warp and some early Linux boots.
Every year or two, I buy a new disk, much bigger than the previous one, and copy it all over, under some folder called "old" or some such.
Then I use removable disks (used to be tape, but now disks are cheaper per bit) for backups, so I always have a few full and recent backups, in different locations.
I've got some old tape, disk, floppy and CD backups, but they are useless. Old stale, unsearchable stuff on media that I probably can't even read anymore. I should throw them out.
* Top Surface: Silver Printable
* Recording Speed: 4X/8X/16X/24X/48X/52X Certified Write Speed
* Storage Capacity: 80 Minutes / 700MB
* Life: 100 years with proper care / read more than 1,000,000 times
In the LONG LONG TERM, keep refreshing data and resaving it.
Pen, ink, and plain ol' paper turns out to be the best for documents after all. Good for several hundreds of years.
As for photos, old family albums date back to the early 1900's and the photos still look good.