I just wanted to note that an interesting alternative to Time Machine is CrashPlan, which is something I'm considering to run headless on my NAS.
For free users you can setup multiple backup targets, including a friend or family member's computer to connect to remotely (if you can get them to set it up and they have space). This option lets you do a mutually assured backup in case one of you has a disaster like flooding or a fire.
Of course CrashPlan's main purpose is cloud backup, which is paid, but it's a good option if you can set-up shared backup or have far more data than your friends can backup for you.
I probably won't use it for local backup as I like Time Machine far too much, and I spent a long time getting rsync setup the way I like for sending a second backup to my NAS (I know I could now use Time Machine for that too in Mountain Lion, but I want actual files on my NAS rather than a disk image).
You can actually do a kind of best of both, by tricking CrashPlan into backing up from your latest Time Machine backup. This involves editing the CrashPlan settings file to point to: /Volumes/<Timemachine Backup>/Backups.backupdb/<Computer Name>/Latest/./
This tricks it into following the symbolic link, rather than just backing up the link itself (and nothing else).
Anyway, just thought I'd mention it as an option, as while having local redundant backups is a good idea, having a backup off-site in case of disaster is something worth considering. As I say, my NAS is actually in a kind of out-building (uses the same power circuit so I can use a Powerline network to connect it), which gives me some protection if the worst happens, but cloud backup is more disaster proof. One of the advantages of CrashPlan is that you can set your own encryption keys; so long as you keep them somewhere safe then it means your data should be nice and safe from the NSA