The question came up recently on my twitter feed of "how often do I really need to backup my Mac"? My initial reaction was that this was some kind of trick question but given some thought and, possibly, a little back and forth in the twitter-sphere I was brought to the conclusion that its a completely valid question; moreso for people not making use of Time Machine.
For those who don't know or took a look at the linked article above and thought (omg, TL;DR) here is the short version. Time Machine is consistently making backups of your data in the background while you are connected to your Time Machine hard drive which means that at any point you can, essentially, jump back in time with a specific file, folder or application. Before any hardcore friends send me any nasty email about being inaccurate, I would like to point out that I'm just giving a brief overview here (cut me some slack)!
But what if I don't want to use Time Machine? I hear you ask. Biting back my obviously fanboy retort of why wouldn't you use it... I've got an alternative for you, it's an application called Superduper! by Shirt Pocket. This little gem will take a snapshot of your whole hard drive and create a copy of it to an external drive which, thereafter, is even bootable. I've used this solution before and I can attest to how well it works: the initial backup takes a while but after that it only updates what has changed since your last backup.
What I currently use as my backup solution is twofold because I travel quite a bit. Firstly, I use a Lacie Rugged 1Tb drive as a portable Time Machine and, secondly, while I'm at home I also use Time Machine to backup to a Network Attached Storage device which I highly recommend. The reason for what might seem to some to be a bit over the top is that I have quite a bit of media, some of which is replaceable in the form of movies and music, but some is not in the form of my photography and other digital creations. This way, if something terrible happens to my gear while on the road where both my laptop and my portable backup are lost I still have a way to get all of my data back.
My opinions on backups has changed over the years and I now consider them to be invaluable; I'm not sure how I ever thought otherwise.