I wouldn't really consider optical media as a permanent option for backups. I believe they are more susceptible to temperature and other environmental factors than hard drives.
I use hard drives with external enclosures for backups. I usually reinstall windows twice a year and when I do that, I'm installing it on a brand new hard drive. The old hard drive is where I put my data on and I remove it from the computer and store it in a safe place. In fact, I'm so paranoid about the safety of my data, I copy the same data to two different hard drives and store one at home and one at work (with the more sensitive data on an encrypted file system). And since Blu-ray drives aren't quite ubiquitous yet, restoring data to a computer without Blu-ray may prove problematic.
I know that over time that recordable optical media can "fade" over time, so I wouldn't consider it a long term solution. Unless you had some type of backup plan where you would refresh the optical media ever so many years, I wouldn't consider it safe for a long term solution.