SuperDuper by Shirt Pocket Software gets my vote for “killer app”. I think this one, $30 program, is almost reason itself to switch from Windows to Mac. Basically it allows you to make an exact copy of your boot drive on an external USB drive. Yes, you can really boot from it. Just start up your Mac with your SuperDuper backup plugged in, and press option when you hear the start-up chime. Then you get a screen asking which drive to boot from and choose the backup. See it really works! Your Mac is running from your backup. You can work on it just like your regular system and you can still see and manipulate files on your internal drive, assuming it isn’t dead.
Suppose you have a system problem, not a drive problem, as I did yesterday morning…my Mac would not boot to ANY drive? Find a friend with a Mac, plug in your backup and boot to YOUR drive as above. Part of what makes this possible is Mac OS. Depending on the age difference between your Mac and your friend’s this might not work, but there are lots and lots of Macs out there that are close enough. In my case, the drive from my laptop booted my friend’s desktop. For starters the two machines have different processors and video cards. On Windows, no way.
You used to be able to do something similar on DOS and Windows, but since Windows 2000 or so, the Windows installation has been tied to hardware and you cannot even boot the system from an exact copy of the drive, unless the drives themselves are identical products from the same manufacturer. Even that isn’t guaranteed. When I discovered this problem with Windows, it meant that all my system backups were basically just data backups and didn’t help me with recovery, i.e. reinstalling Windows and all applications. I started keeping a second machine with identical applications and data synced to my main machine nightly. So in the case of catastrophic failure, which seems to inevitably happen in computerland, I had a system to work on immediately. It is true if you don’t have a spare Mac sitting around you can’t get to work quite that fast, but with a SuperDuper backup you are way closer than you are with a Windows install DVD, a data backup, and a pile of application installation CDs.
That is why I say SuperDuper is a “killer app”. For a fraction of the cost of a second machine, and infinitely greater portability; think 4-3/4″ x 3″ x 1/2″ pocket drive, I have nearly equivalent protection. That is not to say SuperDuper or a second machine protect your system 100%. Neither will help if your main system and backup are stolen or are in a single location that gets hit by flood or fire or lightning, or if you reproduce a virus or system error on both your primary and backup. But either is a big step in the right direction.