Have you got some old backups living on DVDs? It's time to upgrade them for real long-term reliability.
The one big problem that people are just beginning to face is the lifespan of DVD backups. DVDs have been great, thanks to a good few gigabytes of storage on a single disc. But a lot of people have now filed them away, like they're a good long term storage option.
Depending on your discs, you shouldn't feel confident of more than 30 years, and as little as 5 years with a bad disc.