There are several features in OS X 10.7 that make a bootable backup disk somewhat redundant including:
The bootable "Recovery HD" that is installed on every Lion boot disk (Reboot while holding down command+R)
Time Machine
The Apple App Store
I actually find all of these options unsatisfactory.
Option #1 assumes the hard drive still works. A recovery partition is utterly useless in the face of a hard drive failure, as I discussed in Virtual1's thread. Sure, you can buy a new hard drive to replace the one that failed...
...but then you have no OS media and so no way to reinstall.
Option 2 requires that every computer user go out and purchase a second hard drive to use as the Time Machine backup. And even then, if your primary hard drive fails, you're just as buggered as you re in Option 1--ok, so you have this wonderful non-bootable Time Machine backup. So what? What do you do now? Without install media, you can't reinstall the operating system on your computer so you can't use the Time Machine backup.
Option 3 doesn't help at all. If you can't get an operating system onto your computer, you can't use the App Store.
So, if your hard drive fails, and you don't have installation media...now what?
