Is CD/DVD media safe for the long term - say 10 years?
I don't think anybody knows, yet. The very first CDs came out c. 1985. These were music disks and they still work today - if not exposed to much humidity or heat.
The first writeable CDs came out c. 1993 (the Yamaha writers then cost £5000!). These are still readable, if stored properly. But that's only 13 years' data we have.
The only storage proven over longer is, believe it or not, good old mag tape. You can get 20GB on a DDS4 cartridge. DLT will do much more, and there are other formats. Most serious businesses use tape even today. Even then, one would recommend rewriting it to new media after 20 years or so.
The problem with CDs is that they are very easily damaged. One little scratch and it's gone. I never use them for serious backups. Digital photos are stored on two separate hard disks, and a DDS3 or DDS4 tape. The DDS tape drives are about £300 now (HP).
Soon, blue-ray DVD writers (30GB?) will compete with tape, for the first time, on capacity. That will change the backup market a bit. but it will be a long time before anybody will trust it for retention life. And you still need just one scratch...