As the trend to abandon video tape in favor of file-based camera recording systems continues, the need to back up your files becomes that much more pressing. Allowing camera original footage to reside on a single hard disc without backup is inviting disaster. And typically the question isn't if the drive will fail, rather the question is "When?".
Fortunately, the price of big hard drives continues to plummet and there are software solutions that are cheap, reliable and easy to use. For instance, a Seagate 1.5 TB USB 2.0 drive goes for under $230. (If you're used to using a firewire drive for editing, this isn't necessary for a backup drive. USB 2.0 is plenty fast and the addition of a firewire port can boost the price.)
For software, you can check out memeo's autosync. I use it to maintain a duplicate of any project I'm working on. Once the initial sync has run, the program only backs up changes you've made which is usually a quick process. Also since it's syncing the drive, there is no file compression introduced. Backup compression isn't necessarily a bad thing, but if I need to restore a file it only entail a simple copy procedure.
At $30 it's also cheap and offers peace of mind and huge labor savings when the hard drive catastrophes occur.