I do two backups to different disks using different software for each backup.
I use TM to one disk and SuperDuper to update a bootable clone on another disk. When one of my disks failed I was able to recovered the needed data using the other backup procedure. it wasn't ideal becasue it took longer but it was better then nothing.
Drives are fairly inexpensive... especially when you consider the value of your data. I prefer to have an external dedicated as a bootable clone (using CarbonCopyCloner or SuperDuper). I keep that clone at the primary location of my machine. That way if I have a failure, I can be up and running nearly instantly without the need to go through any sort of recovery process. I keep a separate clone offsite (incase of a fire, flood, other catastrophe that may destroy my Mac and my local clone). TimeMachine is great for capturing those incremental updates. I'm sure most people don't keep several copies of their data (and I'm sure there are folks that keep more than I). At a minimum, you should have some form of backup besides (in addition to) TimeMachine.
I keep one hard drive dedicated to Time Machine backups, for more of a "convenience" backup. Then I have two more drives, each one with a clone of my hard drive created with Carbon Copy Cloner. One of those drives lives in the safe deposit box at the bank, the other at home. Periodically, I swap the two, so that the one at the bank doesn't get too outdated.
I pretty much do a similar thing, but my offsite backup goes to a locked cabinet in my office (easier to get to weekly to bring home and update then using a bank - I honestly cannot remember when I last physically went to my bank, its been years).
TM makes a great source for restoring single files or being able to go back to an earlier version of a file. And the clones are easier for full restoration, or even for booting from temporarily if the machines boot drive dies and you just want to get in to deauthorize it before sending in for repairs or such. Always good to have a bootable clone around, for many reasons.
My external clones are on firewire 800 bus powered portable drives, again for simplicity (no power cables or bricks to go with them).
I also still burn to optical disc for specific things like filed tax returns, and other financial documents I need to keep around in the fire safe for some period of time.