A good backup plan is essentila these days, not just for your PC, but also for your smartphone. Optus has just launched Smart Safe, an online backup solution that lets customers back up up to five PCs or mobiles to the cloud.
Gus over at Lifehacker has been testing the service out, and while it's a little buggy, it also seems to be fairly decently prices. Current Optus mobile customers get 500MB free (although data transfers are metered), while a $5.99/month option gives you 10GB and $14.99/month option gives 300GB, and both paid options are unmetered.
For peace of mind that your important files are safe, there are probably cheaper options overall, but if you're an Optus customer, the convenience of unmetered data transfers may sway you to this service.