I've just switched to backing up using Apple's Time Machine. Previously, I used Retrospect for nearly a decade, which was perfectly serviceable. But Time Machine is by far the most elegant and intuitive interface I've ever seen or could imagine. The trick is the fact that we have lots of data... over a TB. So Apple's Time Capsule doesn't work, since it's 1 TB. I ordered two of LaCie's 4big Quadras which contain 2 TB each in the default configuration. Imagine my frustration to discover that external drives don't work over a LAN! That was a couple grand thrown away! But then one of the Apple tech support people clued me in to the third-party utility iTimemachine meant for MacBook Air disks that he'd heard activated all external drives as Time Machine LAN backup drives. It worked!!! So now we're running Time Machine on a two-disk backup set, and life is good! Or, when it isn't, it is anyway.
I had been using Time Machine to do our backups for a little less than a month when the first backup disk filled up. I'm embarrassed because I hadn't counted all the disks in the office that need to be backed up, and 2 terabytes of disk space on the laCie 4Big Quadra simply wasn't enough. Fortunately, the laCie return window hadn't yet closed, and I hadn't even opened the box of the second drive. So I was able to pay the difference and get a couple of 6 terabyte drives instead.
The problem stemmed from Time Machine's voracious appetite. If you have an external disk plugged into any machine being backed up, it'll assume you want to back up the external disk unless you explicitly tell it you don't. That's generally a good thing in a backup setting, because you'd prefer to catch too much stuff rather than not enough. But just make sure you have enough disk space to support the habit.
One other thing... my Catalog of the Most-Loved Places had outgrown the 350 gig laCie Rugged drive I carry around with me, so I got a 500 gig Rugged for the images, freeing up the 350 gig drive. It occurred to me on a recent trip that because the drive is nearly double the size of the hard drive on my MacBook Pro 17, it should work for a Time Machine backup. Sure enough, it works like a charm! Then when I get back home, I simply switch disks in the Time Machine control panel, and I'm backing up to the office 4Big Quadra instead.