I've never used Time Machine.
I never will.
TM is a flawed concept that lulls users -- particularly newer, unsophisticated users -- into a false sense of security about backing up.
The impression one gets from TM is that "backing up is now so easy!" -- just plug in a drive, turn on TM, and don't worry.
It seems true on its face -- the "backing up" part of the equation does seem easy. It's the "getting your data back" in a "moment of EXTREME NEED" that trips up Time Machine.
I'm going to guess that a near-majority (or greater) of cases in which an "average user" needs to reach for the backup volume is when he/she tries to boot up and...... the Mac won't boot. They may try to start up from their TM backup and... what next?
Since a TM backup isn't bootable, you can't just "boot from your backup" and get going again if your "main drive" won't give you a boot.
And TM doesn't store files on the drive in POFF (plain ol' finder format). You can't just "copy over a file" you need in an emergency.
How do you accomplish such things easily when you can't get booted from [usually] the only bootable drive you have (the one that is damaged)?
Time and time and time again, I've seen postings here on MacRumors from users asking for help with TM. Typically, they've had some kind of failure and they're trying to access their TM backup and can't get to it.
If they had had a "bootable clone backup" from an app like CarbonCopyCloner or SuperDuper, they'd be up and running again in a matter of a couple of minutes.
Yes, I know the response you're going to type next:
"TM and CCC are designed to do different things", etc.
That may be true, and I can see instances where having a TM backup may be worthwhile to someone who is just trying to recover an earlier version of a document they were working on (it should be mentioned that CCC can now "archive" older versions of files that are normally removed during an incremental "clone").
But usually, folks are trying to recover from a crashed drive, a mis-initialized drive, a corrupted partition, or the trashing of an entire folder full of data. In these cases, a bootable backup -- even if the files aren't "current" to the last several hours or even days -- is far preferable to a "last minute backup" that can't be booted from.
This may change a bit with Lion's "protected recovery partition", but even that has limitations in that it contains only a few things to get booted from, and I doubt that you'll be able to add anything to it.
NOTHING beats having a relatively recent, bootable clone of your internal drive with everything on it.